LMAO that went dark hahaha
Yeah, the theory comes from some pokedex entries and other similarities. Like they weigh the same, the color and size are roughly the same. And they are the only ones that can transform into other pokemon. There is a whole bunch to this theory and it goes a looong way back. It's actually surprising how many hidden gems and easter eggs are in that universe, there is a whole range of them, from inside jokes to deep philosophical and existential questions.
Anyway, I got to return the favor: 