I do not practice in OR, but normally, the person who was the "handler" (your roommate) could receive a citation (ticket) for the incident. The owner of the other dog could name both you and your roommate in a civil suit for damages to the other dog. If there wasn't any provocation by the other dog, then you would be responsible for the veterinary bills.
This is not to be construed as legal advice. I do not have an attorney client relationship with you.