That's some crappy cookie / tracking crap right there.
I thus did not read the article, but for me single board computers usually sports an OS, microcontrollers don't.
More?
The first have at least 0.5GB RAM (up to many), several cores, and somekind of hard drive simila : onboard + SD card and runs sole Linux flavour.
The second is usually a single core processor with all it needs in it. Like up to 256KB ram and that's about it. Program it over some serial or usb link and it just runs when you apply power to the board.
Edit: up to 256KB! I have some with 32KB for example
It's because usually there are no graphics on these small beasts so it's basically all for (your) running code.
I saw in the answers (funny you get so many because of a typing mistake:-) there are effectively weird ones with loots of memory, IDK what their usecase is for.