A lot of sunflower seeds can look very similar. I wouldn't let that concern me.
I'm familiar with Mammoth, but not Skyscraper too. Sometimes...(but this may not be the case) a seed company will rename something to make it more appealing...or seem different to consumers. Like I said...this may not be true of this particular variety...but it's something to be aware of.
Looking at the photo of 'Skyscraper' on Gurney's website, it looks like it has numerous flower heads. When I grew 'Mammoth' (many, many years ago) I remember them producing just one or two very large heads. I've never grown 'Skyscraper'. There probably is a slight difference in the taste of the seeds. Maybe someone can distinguish the characteristics further than I. :-)