That's true, once you start fantasizing about things it can be the death of your productivity in the present moment. It's a common behavior for depressed people. It makes complete sense to me that Rafa is telling the truth here and I don't know why he'd lie either. It just lines up with his attitude towards life in general. I think it's way more likely that people on a tennis forum would think more about it than the actual players and that's why it's so unbelievable to them. I can understand why they might think/suspect Rafa is lying but you can't be 100% sure of that.
We all engage in a bit of "self-BS" from time to time, and some of it is probably necessary to stay sane.
If every time someone asks you "how is your day" and you don't answer with the exact truth, with all details, that doesn't mean you are liar.
If you are famous and then bombarded by invasive questions from the press, every day of your life, only a fool expect you to answer every questions with the complete truth.
I don't agree that famous people are obligated to answer every question every time politely.
Just one I'd like to hear a top player say, in a press conference, to someone especially rude:
"You know, that's a REALLY stupid question, and if you ever again ask me something that dumb again you'll never get an answer from me again in the future. Now, does anyone else in the room have something intelligent to ask, or should I end this clown show right now?"