That, or it's a generic store bought cake. It isn't even a pride rainbow coloring, just random non-white frosting with a splash of color, like most yellow/white cakes. So, even if he is Gay or Bi, I doubt the cake is meant to even remotely signal that.

On that note, that's like a cake you give to a little kid, do they still think he's 5? Then again, maybe that's what he likes, it would honestly check out and explain a few things.