I don't really blame the girl, if she didn't know OP and his schedule she could've genuinely thought that he WAS stalking her - a bit paranoid, but not reprehensible in itself. She was also right to tell her teachers, because if he had been a stalker, asking him about it wouldn't really have been an option. I do blame the principal, because he could've easily checked out OP's explanation and then told the girl that everything is fine and there was nothing to worry about.