An odd argument to say the least. Playing a ps2 game on a PS4 isn't backwards compatible.. because it is digital?
What do you call playing older generation on new generation consoles that are digital if you are gate-keeping the phrase backwards compatible?
Very simple, I would have to REBUY that game digitally to play it instead of just popping my disk in and playing. You cannot put a PS2 game into your PS4 and play it, so it is not BC.
You are basically being forced to rebuy emulated ports of games you already have. By your logic, one can say the Switch is BC with the Wii, GC, and N64 because Super Mario 3D Allstars is just a compilation of emulated ports that we have to rebuy.
So again, there is no BC on the PS4, and only PS4 BC on the PS5. Backwards compatibility and digital ports you have to rebuy are not the same thing, and honestly seems like a desperate attempt at downplay to what MS is doing.