I have a Stratux box (ADS-B in) with iFLY GPS software on a Samsung tablet. The other day I had a close encounter with another plane that came within about 1 mile of me at very nearly the same altitude - VMC conditions. He was overtaking me, and I was on an IFR flight plan. The app indicated zero (to slightly low) altitude delta and was showing red at my 6 o'clock. This caused me great concern so I called ATC, who indicated that the other plane was VFR and he was not talking to him. I climbed to move away from the other plane.
After the flight, I reviewed the ADS-B data which indicated that the other plane was actually at 5500, while I remained at 6000'.
Question: Why did the iFLY indicated zero altitude delta when the recorded ADS-B data indicated otherwise? Why didn't I see the actual (GPS/ADS-B data) 500' delta indicated?
See attached Google Earth view.