Phantom Plane?

Maybe I’m a total n00b and am missing something as the kids would say. I’m using the iPhone app to track planes at the moment. Call it working a late shift at with nothing better to do.

But at 2015, I heard a really low plane directly overhead and nothing in miles on the radar. I step outside to see what appears to be a B73x low. I mean low. Usually low around here is 8-10k feet AGL. He was struggling to climb by the sounds of things. It was so loud that I was waiting for it to literally drop out of the sky.

This guy I am guessing was around 3k AGL heading west directly over head. Nothing within 40 miles looking at the radar heading west. Nothing at all under 7k. (Th only thing in 15 mi under 7k was a south Cessna for FDK.

My thoughts are it is an NW B73x for PIT from BWI though they seldom fly anywhere near that low and never over this flight path. I did find an NW flight for PIT from BWI appear on the radar about 20m after the plane I saw but the raft showed it still 10mi east of my location and at about 15k.

Is this normal for the FA app to miss something or be this far off the mark? About 12k and 30 minutes?