This is about questioning assumptions. The knee jerk reaction prunes qe4+ from the space of possible solutions because bxq. Then the mind is drawn into analysis of other possibilities, e.g. rxf8+.
Indeed, I wisely threw away Qe4+ because I knew the mate was with the Queen somehow. And spent the next 8 minutes staring at every other line. I was getting ready to contemplate fairy pieces and non-standard castling rules. Or which piece my friend decided to forget in the original. Again, nice puzzle!