That is certainly possible. When you walk in on the middle of a class and expect to get attention it would be a lot like walking onto a farm while the farmer was busy doing his/her job and expecting them to drop everything for you. People who don't give respect often don't get respect.
“When you walk in on the middle of a class and expect to get attention it would be a lot like walking onto a farm while the farmer was busy doing his/her job and expecting them to drop everything for you.”
Except that a public school is not the teacher’s private property. And even if that were not the case, the teacher has no excuse for being rude. Unless the visitor is putting people in danger, the teacher should exhibit some grace.