Speculation: She probably indicated it was a service dog during the initial call and got the "I guess it's OK". Then she didn't clarify that it was a service dog when checking in. It may or may not really be a service dog but she clearly created the issue with poor communication.
I thought I saw some statistics suggesting small dogs do bite more. It's not the breed but the owner. In simple terms, if your chihuahua goes after the neighbor kids, there's typically a bandaid applied (if they even manage to break the skin) and you applogize to the parents. If your rotwhiler goes after the neighbor kids, there is a hospital visit and the authorities are called.
It's wrong not to train your chihuahua not to bite but reality is it's far less of a critical issue. But if you dont' put your hand next to his mouth, the chihuahua really can't get at anything he can get his mouth around.