Knight v Bishop (part 55)

White has just captured on c3 in Winfried Natterer (1811) - Spanton (1924), Bad Wörishofen (Bavaria) 2015. Who stands better, and by how much? 

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Black has a good knight against a bishop restricted by many of its own pawns but that has a target in the a5 pawn. The analysis engines Stockfish12 and Komodo12.1.1 reckon the position is dead-equal.

48...Ke7

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49.Kd3

49.Bb6!? Nxh4 50.Bxa5 keeps the position equal, according to Komodo12.1.1, but gives Black a slight edge, according to Stockfish12.

49...Kd7 50.c4 Kc6

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51.c5??

At the time I thought this a stunningly bad move with no plausible explanation, but I guess WN's idea was to prevent ...b6.

The game finished:

51...Kd5 52.Kc3 Ng7 53.Kb3 Nf5 54.Kc3 Ne7 55.Kd3 Nc6 56.Be3 Nb4+ 57.Ke2 Na6 58.Bd2 Nxc5 59.Bxa5 Nxa4 60.Bb4 Ke4 61.Bd2 Nb6 62.Kf2 Nd5 63.Kg3 b5 64.Bc1 b4 65.Bd2 b3 66.Bc1 Nxf4 0-1