The oil pressure sending unit, that would have caused the light to come on if the oil was low, is located out of the way of the oil filter and oil drain so it's unlikely the mechanic did anything to disturb it during your last oil change.
Sounds like the unit itself might be faulty. Looks like you might be taking it back or keep going and maybe it was just a one time happening. It's up to you.
It does sound like you did pick up somebody else's problems.