I had a similar issue. A teacher found me with a smaller boy (poor kid had some genuine emotional issues, in retrospect was probably being abused outside of school) who was nevertheless doing his best to rip my ears off. The fact that I had my hands on his wrists was seen as reason to split the resulting punishment between both of us.

These days I pin a lot of this kind of thing down to the psychology of teachers, which seems to skew hard towards an unmet desire for respect/authority coupled with a relatively dull intellect. Most just aren't equipped to take charge of children.