2015 Honda Accord with 170k, Check engine triggered by fuel cap, but there is just "permanant" codes living in the computer?

Few days ago, my dash sends me a message to check fuel cap. Checked it, seemed fine. Happened again the next time I started the car, check it, seemed fine. Have not seen it since turning on my car, but this morning the check engine light came on. I assumed it was because of the fuel cap, went to Autowhatever and plugged in OBD and it showed me five codes, one "P0420 (permanent)."

Has my car's computer been registering an o2 sensor/cat issue that it hasn't decided was check engine light worthy?

I understand that at 170k my cat is probably toast, but did the fuel cap just trigger the light and I'm seeing information I would have been none the wiser to?