I mean, it is certainly a gross oversimplification, but the principal is actually the same. Pump enough electromagnetic radiation into something, and it’ll warm up. Microwaves, visible light, gamma rays, radio, x-rays, uv, infrared. It’ll all work the same way. Now, shorter wavelengths than visible light will also give you cancer, or radiation poisoning in high enough doses, but microwaves are actually longer wavelengths than visible light. They’re actually less dangerous than a flashlight. There is that whole bit about the actual kitchen devices being powerful enough to cook meat, so I wouldn’t recommend sticking your hand in one or anything, but only because it would be cooked.

There’s also stuff about Faraday cages and standing waves and crap, but that’s not really important to the point I was making. The only thing less dangerous than microwaves are radio waves, and those are just physically too large to fit in a little box in your kitchen. Seriously, you can’t have a wave trapped in a box smaller than the wavelength.