HVAC Fan on without Key

Apologies if this is in the wrong forum. Please move as required, thank you!

I've been figuring out how to get my dash cam to stay on after the ignition is turned off. I have an old Apeman dash cam (but I don't think that's important) on one of those Donger adapters coming off of the rearview power in my Limited.

My idea was to get a small USB battery pack and put it inline between the Donger adapter and the dash cam.

Weirdness starts here:
I plugged everything together (Windshield power to Donger adapter to USB power pack to Dashcam) and suddenly the HVAC fan comes on! I can't get it to turn off without turning the vehicle on and then turn it off again.

More weirdness - I confirmed that the batter pack would work with the ignition off. The dash cam stays on so all good. I go to close the door and lock the car but it keeps saying "Key not detected" in the display. I turned the vehicle on again and turned it off. Made sure it was in the off position and got out of the car and tried to lock the door again. Same thing - Key not detected.

I unplug the USB batter pack from the dash cam and connect the dash cam back straight to the Donger adapter. Problem solved - door locks again, no more messages on the dash.

I'm not sure what it is about having the USB power pack plugged in that's causing the vehicle to behave in such weird ways.