How does a screen work?

> modern displays don't paint the image line-by-line (...) They light up each pixel simultaneously, refreshing the entire display at once.

The entire screen area is lit all the time now, yes, but refresh still typically happens line by line, top to bottom [0], left to right [0], for both LCDs and OLEDs. It's a scanning refresh, not a global refresh (sadly).

You can experimentally confirm this using a typical smartphone. Assuming a 60 Hz screen refresh, recording in slow motion will give you enough extra frames that the smartphone camera also likely operating in a scanning fashion (rolling shutter) won't impact the experiment. On the recording, you should see your screen refreshing in the aforementioned fashion.

[0] actual refresh direction depends on the display, this is for a typical desktop monitor

But you're right both LCD and OLED refresh a stored voltage on the cell (or caps) on a roughly line by line (OLED can easily be 5 clocks on the GIP to cancel internal transistor offset voltages).

I was mostly annoyed that they didn't mention the circular polarizer on OLEDs. Although there is discussion of going to color filters with Quantum Dot OLED, the circular polarizer is what makes the blacks so black on mobile OLED devices.

Also, didn't really mention pentile RGGB sub-pixel pattern which is dominant in mobile OLED (which is more than 50% of devices). Now they're moving to "tandem" stacked OLED for higher brightness and lower current density, but no latteral sub-pixel pattern.