Considering the theme of "insects" for Ant-man, and the lack of HYPE for the movie itself, I wouldn't be surprised if that is where they post credit Spidey to boost ticket sales.
With the 6 legged look of Yellow Jacket, I wouldn't be surprised if Pym ends up trying to recreate the SS serum, gamma radiating it, and testing it on a rare breed of spider when an accident happens.
So his consolation for not being the baby daddy of Ultron, is getting the credit for creating Spider-man instead.