My old oil filter looks brand new...why?

Alright, I'm confused.

I've had my mustang on the lift for about 5 days doing a T5 swap and I figured I'd change the engine oil today. So I drain the old oil (which was black) and then put the drain plug back in and unscrew the old filter. The filter didn't look too bad on the outside. I suppose I didn't drive the car too much after the last oil change (the mustang sat for a year). I get the filter off and it is almost completely clean! No oil residue or anything. It's like oil was never run through it.

I have run the car for at least a few hours since I started working on it recently. The car runs fine with no valve noise or anything. Is there any reason the oil filter would be bypassed? Should I be worried?

Ya, I checked all the gauges quite frequently for a good 20 minutes when I started it up for the first time in a year to make sure everything was ok. Everything read normal. I didn't hear any engine knocks or clattering. Everything seemed perfectly normal.

I looked into the filter a little better and found that the bypass valve in the filter did have some signs of oil on it. I suppose it's possible that the filter completely drained out in the 5 days I had the car sitting on the lift....it just strikes me as weird that no loose oil came out at all when I placed the filter upside down and shook it about and whatnot. Oh well. I suppose I might reuse the filter and just do another oil change once I get to CA.