This is easy to figure out ... go to Delta.com and see if you can book a seat on the flight. If DL is still selling seats; then the flight is not "oversold".
Well if I could have still booked a Y seat on the flight, that would have meant I could have used Same Day Confirmed instead of Stand-By. Thus, the flight was "oversold" "overbooked" but still had room for passengers.
This is why this place is so annoying sometimes. Everyone understood the context of the discussion, but people need to offer their 2 cents on the intricacies of an airlines exact terminology.