Hi jeffrey
I suspect that was what happened. If he looks normal in every other way, chances are that he was very sick at some time and you didn't notice.
Give him a good looking over to see that his tail and fins look sound and he has no white patches or anything at all odd about his appearance, (except for the barbels, of course), just to be sure he is OK now.
Bacterial infections are perhaps the leading cause of death among corys and keeping your tank water clean and fresh is the best thing you can do to prevent them.
Barbels are sensory organs that corys use to find their food. If they have eroded to the point where they are gone, it's going to be necessary for you to watch him to make sure he is actually getting enough food to eat. It's not impossible for him to regrow them to some extent, but you will have to wait and see what happens.
Feed him a diet high in protien, with live or frozen blackworms, tubifex or blood worms to help him regrow this tissue and rebuild his immune system after being sick.