I have had something similar happen. I caught my Black Pastel het Hypo gal eating a rat that was still kicking a bit. It was odd to see, but there were no ill effects. I reckon she was just in a hurry. Also, I am sure it happens a lot more often than we think, but we just do not catch it. I made sure when I fed her any live after that, that after she coiled I would pull on the tail and make her REALLY coil it. No problems after that (and she is on F/T now).
As for the folks that go on and on about ALWAYS feeding F/T, when you have enough animals you will run in to some that will just not eat F/T, or you may be in the process of transitioning (there are also several other valid reasons that some folks feed live, but that is neither here nor there).