I am a total newbie in chess. I was playing with an ~intermidiate computer~ as White and made a pretty stupid mistake by playing Bf4. I waved the bishop goodbye, yet Black's rook did not capture it. Was there any good reason for the Black not to? The white pawns are moving downwards here. As far as I know, the pawn cannot move back to capture, so I reckon the bishop to have been 100% unprotected.
[FEN "8/4R3/8/4P1B1/6k1/PBP5/1P3r2/1KN5 w - - 0 1"] 1. Bf4 Rf3