Gen 11:10-11 These are the generations of Shem: Shem was an hundred years old, and begat Arphaxad two years after the flood: And Shem lived after he begat Arphaxad five hundred years, and begat sons and daughters.Shem's other sons are not mentioned here.
No....you are correct, but....it is mentioned that he did have other sons, whereas Cain, a central figure in Genesis, is no where mentioned in Adam's genealogy.
You cannot even include Cain among this other progeny as it transpires after Seth: [Genesis 5:4] And the days of Adam after he had begotten Seth were eight hundred years: and he begat sons and daughters.