That does not look OK at all.
Better let him check with a vet.
Could be an infected wound or something,
guess when i would have this on my back i would be running to the hospital
My best bet would be something like a bacterial infected wound, burn or not.
Looking at the edges of the wound, this isn't something that will heal overnight,
it is a nasty flesh wound.
Or the picture must be decieving me.