I honestly don't understand how traffic settings work in this sim

I have all AI traffic disabled. What this plonker is doing here? Judging by the abomination of movement he did next it definitely was not a multiplayer a/c.

Sure multiplayer has been deactivated? That would be my first thought.

That wasn’t multiplayer. Besides, I heard tons of AI reports on the default ATC.

I’d suggest temporarily turning “Show Traffic Nameplates” to ON to help identifying the aircraft source.