You did absolutely right thing, I don't see anything inappropriate. Cafeteria is the school property. I think the principal should be grateful for your to point out. If anything happens, the school is liable for students well being on campus.
In the other hand, I have encounted so many school teachers and staffs, who have no work ethic and poor moralty ( they come to clinic asking for job excuse or sick leave for self gain, etc. ), Parents have to take the responsibility to make sure school do their job.
Strongly support you!
