I would guess there is photocell next to the LED and comparing the amount of light to the ambient light the cameras get. They might also be doing something clever and using the LED itself as a photo diode.
It looks like the connector just happens to fit so it's only being used to make the electrical connection. The 4 pins are actually power, ground and I2C data and clock.
This looks almost identical (though maybe a bit more stripped down, haven't looked closely) to the Orange Pi Zero which has been on sale for a few years at a similar price.
If you're not already familiar with Soft White Underbelly (interviews and portraits of the human condition), I highly recommend checking out Mark's other videos. I particularly enjoyed the recent series of folks from Appalachia.
I've been really happy with a similar Cannon printer (Cannon G3200).
The print quality is quite good, it comes with an insane amount of ink, and you literally buy full replacement bottles of ink and pour them in the tanks.
No artificial page limits, no checks for non-oem ink.
The major credit card companies have a service where they can notify the merchant of the new details when the card expires. I believe Visa calls it Account Updater.
