Which means the teacher probably reacted to the noise and was not paying attention to anything that went on before it. Ever hear a loud bang and not what led up to it?
Eating lunch. Reading a book. Not looking directly at 3 girls just walking by a table. You can't expect someone to be there the first 3 seconds of an interaction. "Why didn't someone open the door before the visitor rang the doorbell?"
I will likely get hammered for this statement...but white women are the second most privileged group of people there are. Just ask any black man or other POC. White women get the benefit of the doubt in nearly every legal situation (even over white men).