How 'wet' was the cloth? If you could wring a droplet of water from it then it was probably too moist. I've never had a problem with my MBP keyboard and cleaning but I did, last week, 'kill' an Apple USB keyboard not because of the moisture on the cloth, apparently, but because I scrubbed on some keys more vigorously than others.
There's probably no way that you can fix the key - but you can replace it and see if that will bring it back to life. Visit -> https://www.replacementlaptopkeys.com/ - and order and replace the key. If that doesn't do the trick you likely got to much moisture and the key corroded.