Wow, nice piece! where did you get such a monster?
I would have to say that yes the slimer probably did that. Was it very close to it? Is there still a lot of slime coming off it (the slimer)? It looks good in the picture. I find it surprising that the slimer could do that as they are usually on the low end of the stinging scale, but with enough slime, I guess its possible.
As for your hammer, the damange is done. You did the right thing by getting rid of any left over mucus. If there is any life left on the head, it will grow back, but whats did is dead.
If the sliming has stopped and they is enough separation between the two then that should be the end of the damage.