>>33774876The difference is that nihilego is still a standalone UB you fight lvl 20something and it flees the battle if you don't 1shot it. Nobody thought it would evolve because there's no reason to.
Instead, Adhesive is a trainer's pokemon and we fight it at Paniola (according to the bakground). The trainer is not gonna flee from the battle and the UB is small and has the appearance of a NFE pokemon. It's not a mythical because those aren't used by trainers and not even available in the game most of the time.
That's the biggest reason for people to think it evolves. Since a trainer has it so early on in the game and it looks like some kawaii desu NFE mon, it'd only make sense that the next time the URS people fight you, they might show up with an evolved adhesive.
Then again, it might mean jakshit, but point is that there's enough logical reason to believe it might evolve
