Theory of Mind in toddlers

I was curious about how one can begin to understand their child's sense of ToM. I've felt like my child is maybe a bit above the curve in terms of mental development (he is already capable of saying maybe 50-60 words, including names of 5 people and one dog, at 18 months old. He can also combine words to make contextually appropriate statements (for example: if I'm getting my coat on, he might say "daddy bye-bye" as if to say "Dad is leaving"). If he doesn't see his mother he might just say "mom-mom?" while raising his arms in the universal "who knows?" position—or he will say "mom-mom gone". I've been around several 18mos and it seems atypical to me that they're capable of these things so early.

Well today he did something interesting. When he sits on the potty he likes to read a book, and just a few minutes ago I closed the door so I could go to the bathroom, and he slid a book under the bathroom door. Is it just automatic? Or is he forming some prototypical sense of "I like to read when I'm on the toilet, so I'll bring one for him since he is on the toilet"?

Edit: I seem to have riled up some negative emotions in the readers on this community, for what reason I have no idea, but for what it's worth: I'm not trying to just brag about my child. If he's average that's awesome. I'm just trying to give context on what I see my kid does and use that to maybe try to understand how his mind works. It's a fascinating subject to me.