In every day usage, anybody teaching anything is called "sensei", whether it be pottery or day care - or hip hop street breaking, whatever. Doctors and lawyers are also called "sensei".
Basically, it just means "teacher" - so it's used for anybody teaching because Japanese are anal about using titles to refer to people.
Depending upon where you are and the culture you live in, that may not be the case.
Also can be used dismissively when one is seen to be acting beyond thier station ... like some 5 kyu shihans, etc.