The MRO's are everywhere. It's usually a side job for them and they aren't chosen by the lab or collection site but usually the employer or whoever's paying for the test. They could be in the town where the collection site was or not. Remember that where you gave the sample may not be where the test was run. "Few towns over" could mean anything.

If you think you have a good chance of failing there is a good chance that was the MRO calling. If you fail for a prescription drug you would probably get more than 1 phone call but 1 call is about average if it's a positive for THC.