Is that "not extremely dry" or "now extremely dry"?
We suffer horribly wet weather here, but even a few days of dryness can make the feet really hard and crumbly-looking. Possibly the coronet bleeding was due merely because of a slight injury, which would normally have been "absorbed" by the rubbery texture of the coronet, but in this case, it cracked.
Perhaps letting him stand in a little mud would help?
I use Vaseline on skin (white nose) to keep rain off; then mineral oil in places to keep skin softer. (I think I just like to fuss!)
I'm glad he's sound. Lots of exercise always seems to "even out" effects of environment.