If the filter wasn't on, oil would be all over the place! I'm gonna ask a stupid question, but it has to be asked. You were doing an oil change, did you put oil in? Sorry, I hate to ask those things.
It isn't an issue with the oil pressure sending unit (or it'* wiring) because when they go out, or there is a short in the wiring, it'll read maximum pressure due to the infinite resistance in the circuit. As such, he'd be seing something like 99psi.
From a mechanical aspect, if you're not getting oil pressure, that'* indicative of pump failure, which by now, if that were the case, you'd also have catastrophic engine failure.
But if you pop off the oil fill cap, peer in with a flashlight, and see if there is fresh oil in there, that means the pump is infact ok, and that oil is getting to the upper portions of the engine.
In which case, it would be indicative of an electronics gremlin