I once thought I was dating this friend of mine while he thought we were really close friends who went to the movies and hung out all the time. He was fantastic and sent me a very nice email saying he heard rumors that we were dating and he just wanted us to be and remain friends. Incredibly embarrassing, and completely unintentional on both of our parts!
Yes, that’s a kind of thing that can happen. People misunderstand each other in all kinds of embarrassing ways, especially since our culture makes it hard to talk about these things explicitly.
Everyone honestly misreads things sometimes. Imaginary friending is different. Imaginary friending is when you are unwilling or unable to consider the possibility that someone doesn’t want the kind of friendship you want. (Even if they’ve said so explicitly).