Sometimes you get a group of loud people around celebrating something, like soccer cup or getting married (especially in the connections with Regionals). Also last year there were often delays and problems in the connections between Mannheim or Frankfurt; I wouldn’t just call someone’s comment rubbish.
While you're technically right, the MUC-BRU flight is 90% businesspeople in suits on the smallest regular plane I've ever used, I can't imaging TXL-BRU being different.
I.e. the chance of it having a school class in it is like winning the lottery ;)