I don't think it is okay to call a teacher at home after hours. That said:
I think what makes all the difference in this case is that the teacher called the mom from her home number, in the summer, before the mom called the teacher at home. Just like PPs are saying they would never call a doc or vet at home after hours, my docs and vets have never called me from their homes either, but the OP did call this mom. I can see how an unwitting mom (maybe oblivious to how professional relationships should work) could make the assumption it was okay to call because she had been called first off of school time from the teacher's home number. It may have been annoying, but I don't think it warrants a creepy-stalker title.
~J, wife to one, mama to three wild and crazy guys and one little lady!~