Sounds like maybe it was a cigarette that set it off?

Not sure what else it could have been.

If it was someone smoking a cigarette in the restroom, they must have been very inexperienced travellers. Or maybe just stupid? Or maybe someone thought vaping wouldn't trigger the smoke detectors? Canada was the first country to fully ban smoking in all Canadian-registered aircraft thirty years ago.

There are plenty of stupid people out there. Some even travel too.

Canuck--yes, it could have been someone vaping. We probably will never know.