I think lips are designed to be durable and not fragile.
I've seen videos where people have bitten another person on the lip during rough sex or intense making out and there's plenty of examples online of impact trauma from accidents affecting the mouth area yet there is no obvious EC.
In my opinion it is unlikely that any mechanical irritation or trauma of a normal person's lips would cause EC. Nothing has ever come up in my research to suggest it starts with trauma. I am not convinced my EC was caused from biting and I've never seen proof that anyone else's has either. In the past I thought otherwise though, I thought I may have done this to myself from rough treatment.
In my case I think my EC has a physiological cause, I just have to prove this with the data. For other people I don't know. Not many people are as willing to find out the whole truth about their EC, they would rather rub stuff on their lips that suppress their symptoms.