All it takes is the whim of one moody, angst ridden 15 year old who decides to make a false accusation to destroy your life.
It's the school / union's fault. The allegation was that it happened in the classroom. Nowadays, there is no reason to not have cameras in all the classrooms.
Sensor tech could be used to figure out how to do education better, and obviously it would avoid problems like this.
unfortunately the article doesn't mention what if any consequences there are for the student who falsely accused this teacher and ruined his life