I am proud to found the way out of this one.

[game;id:1302958;move:16]

blue to move and win (backwards capture game)

wouldn't 17. c5-d5 have done the trick too?

Well that was not the best move to make. There was a slim (1/36) chance for red to win.

17.4/b3-c2 18.x/d3-c3 19.1/c5-c4 20.x/c3-b4 21.6/c4-d4 22.x/b4-a5

The move 17. c5-d5 does not give a certain win either. I think the only winning (that give a certain win with perfect play) moves are 17.4/c5-c4 and 17.4/c5-d4.

I think the reason why you like that move is that it led to the zugzwang position after move 19 which is a win for red under standard rules but a loss in Backwards capture.

[game;id:1302958;move:19]

Indeed, I was happy to find an almost certain win that would have lost the game with standard rules