Hmm, this is indeed interesting. Why does it work for me and not for you? I'll do some more testing, also with another card reader and see what happens.
Update: Just did some more testing with a different card reader. The first time I inserted a card into this reader, Photos started. I then opened Image Capture and selected PM as the app to open for this card. I then quit both Photos and Image Capture. I ejected the card and then reinserted it. PM opened nicely and offered to ingest the card. Photos did not open.
I again ejected the card and then formatted the card (in a camera I hadn't used before). Reinserting the card started PM again, but Photos still did not show up.
So why this doesn't work for you is really a surprise. On my system, the opening of Photos seems to actually be linked to the card reader, not to the card/camera. Why it isn't so for you, I have no idea…