Main reason why this was botted is because of these fall-thru maps. Bots probably just find these maps and then play them looking several seconds into the future and choose actions that will move them closer to the coin. I believe, it is much harder to complete usual map with bot because sometimes you need to actually move in opposite dirrection from the coin.

What can we do to prevent bots?
1. Change level generation algorithm to prevent fall-thru maps. This is the main countermeasure against bots.
2. Increase map size.
3. Use some sort of Scrypt/X11 in map generation to prevent fast map enumeration.

This will definitely take some time to implement.