I'm not sure. They may want to take an extra or do a biopsy of the swelling to really find out what it is. It may not have to do with the root canal but it may be the crown's fault if there was a crown placed on it. Luckily its symptom free so thats good. I would go get it checked out anyways since it is an unusual symptom and its best to find out whats causing it. You can discuss with your dentist abiout a referral to an oral surgeon.