Can a seized calliper be caused by sabotage?

Anything is possible, as sabotage goes it seems pretty unlikely to me as 1) it's illegal, unethical and few mechanics would take that risk and 2) it's not something they are going to make a substantial profit from. They'd have to jack it up and take the wheel off to get at it in order to mess with it, which takes time, all for a relatively minor profit.

Much more likely is the caliper was seized for some time, and you just didn't realize it. A partially seized caliper will stop a wheel hub turning pretty quickly, but will still allow movement. I had this happen on a Porsche 944 I was restoring, once I replaced the caliper I noticed a difference in driving experience.