I'm kind of surprised the demo UI is macOS. Are they mainly using Apple products to develop these things?

The more advanced devs all use apple laptops, sure.

Who isn’t?

I'm slapping debian on any crap hardware around, but that's just me with different ideological standards.

Even better to slap Debian on a 2nd hand ThinkPad :)

Also, Mario Zechner wrote libgdx and his first book on a netbook IIRC.