It seems that there are varieties of Nerium that are root hardy to zone 5 with protection. Calypso, Hardy red, Hardy white and Hardy pink were all touted as such. Perhaps the wall the plant is growing against affords that protection.
Please note woody base, several branches and whorled leaves seen on many branches. Sunnyvale where I live presently has Nerium oleander almost everywhere and it is hard to mistake any thing else for it.
I side with the Solidago family. A picture of it nearer to blooming would help. All kinds of Goldenrods are very common here and grow in the most unlikely places - such as roof cornices of buildings and cracks in walls.
Please have a look at second prominent branch (and many others if you look closely) from left, three leaves from a node can be easily seen. Even if shrubby habit can't be recognised by many from the above photograph, I wonder Solidago, a genus with alternate leaves, would have any member with whorled leaves (for that matter, Compositae which although being largest family of angiosperms, has only a few members with opposite leaves (not to say in whorls of 3) that can be counted on fingers.
I still go with Nerium oleander.
Lancaster PA is USDA zone 6a (winter lows -10°F to -5°F = about -23°C to -20°C). The "hardy" cultivars of oleander barely survive locally here in zone 7b (winter lows 5°F to 10°F = about -15°C to -12°C). In mild winters they get lots of foliage burn and in cold winters they can be killed almost down to the roots. Also, as Resin noted, the base of the plant is green which indicates something herbaceous. So, I don't know what it is, but it's quite unlikely to be oleander unless is a young plant that was recently planted.
The posted picture is too small and too low-resolution to positively ID the plant. We don't know where/when the picture was taken or the size of the plant. There has been no follow-up from the original poster kamjong and unless the OP gives us some more info this one is going to be unsolved.
I don't see anywhere on either of those sites where it says that oleander is hardy in PA? Note that the first site you linked to has a very similar page for tropical hibiscus in Lancaster, PA and I think you'd agree that there's no way those would survive winters there. http://local.garden.org/Hibiscus_Lancaster_PA-r1216504-Lancaster_PA.html So I think that site is just a collection of articles that they probably make available for a number of different cities without regard for whether the plant is actually hardy there or not.
The reputable sources I've run across for the hardier oleander varieties (hardy yellow, hardy pink, etc) typically list them as hardy to zone 7b...I could see that maybe if it was a mild winter and they were in a very protected location they could survive a winter somewhere a little bit colder, but I still think it's unlikely that they would be reliably hardy in PA.
It would be nice if the original poster would come back and give us some additional info/pictures, otherwise I think everyone can argue on and on but there's no way to be certain what that plant is. The picture of the house looks like it has stucco walls which I've seen a lot more of in warm climates (CA) vs the colder climates I used to live in (OH & IN) so I wonder if the house is somewhere other than PA--if it's in a warmer climate then oleander becomes a much more likely possibility. I know kamjong says the plant is at his/her house which would suggest it's in PA, but I've seen other cases where people don't have their correct location in their profile so it would be good to confirm.
I would be most happy to know the true identity of this plant after several members wrote that oleander can't grow in Lancaster, PA, because write now can't think of any thing else. Hope the original poster comes to our rescue with more close up images especially leaf insertion and shape, and flowers to nail it.
It is not uncommon for folks to post images of plants from places other than they list as their home/location.
In this instance, kamjong likely posted this plant image from some other benign growing zone - possibly a second home in Florida or California, but not Lancaster PA unless this was just growing there for one summer season.
My parents grew Oleander in a big container for many years, but it was always taken inside for winter months - or it would've been toast.
That is why I suggest forums to make mandatory the place of photograph. It greatly reduces the job of experts. It also helps in data entry. I have lived in both temperate (Kashmir) and tropical (Delhi) places for longer times to appreciate differences in plants of two climatic regions Perhaps this is a test case that should make the owners of this website to declare place as mandatory. May be a mandatory window for place in upload form should solve this problem. It is much more beneficial for data inventory on any website.