I asked a similar question once. When we moved our tanks from one house to another everyone freaked out and hid in the same corner - it just happened to be the corner our crispa's in. Our yellow watchman goby was there too, with quite a few tents. touching it, but didn't seem to be reacting. We gave it one last scare out of the corner and it was fine.
I was told that they really don't have the option to sting or not, the mechanism fires on contact. But here's what I think happened, and I could be totally off so take it for what it's worth.
I've noticed when our crispa stings/touches things the tentacles turn greenish and shrivel a bit. I don't know how long it takes for them to build up the nematocysts strong enough again, but I assume when the tentacle looks normal again they're on full power.
I wonder if, in your case, so many tents had already fired off nematocysts because it was eating (and has to fight off the occassional shrimp) that the fish got lucky and didn't hit too many, realized what kind of stupid thing it was doing and got out
I've noticed my bta's tentacles shrivel a little like the crispa when it's touching food, so I assume the same thing is happening with it too.
These are just the thoughts of a person that spends way too much time in front of her tanks, or in front of the computer trying to learn more about what's in her tanks, so take it for what it's worth, and wait for more opinions
Glad things turned out okay with your fish!