Yep, I had a very similar thing happen. In the thousands of deli cupped snakes I have only seen this ONE time. Only difference in my scenario was that his tongue was stuck and he pulled so hard on it that he actually ripped his tongue off. I was utterly horrified when I found it and took extreme care of the individual but I believe he was too injured from the incident and ended up dying. I now look at all the holes in the deli cups and if there is even a tiny little burr or spur I toss it. Sad thing is I never could visually find any reason for why his tongue got stuck.
I wish you the best of luck.