Those aren’t microwave safe then, other materials react as well but microwaves are tuned to shame water really well and most everything else not as well.

Yes it is. Microwaves came from radar and radar works on the same principal.

Ed:

In 1945, the heating effect of a high-power microwave beam was accidentally discovered by Percy Spencer, an American self-taught engineer from Howland, Maine. Employed by Raytheon at the time, he noticed that microwaves from an active radar set he was working on started to melt a Mr. Goodbar candy bar he had in his pocket. The first food deliberately cooked with Spencer’s microwave oven was popcorn, and the second was an egg, which exploded in the face of one of the experimenters.[12][13]

To verify his finding, Spencer created a high-density electromagnetic field by feeding microwave power from a magnetron into a metal box from which it had no way to escape. When food was placed in the box with the microwave energy, the temperature of the food rose rapidly. On 8 October 1945, Raytheon filed a United States patent application for Spencer’s microwave cooking process, and an oven that heated food using microwave energy from a magnetron was soon placed in a Boston restaurant for testing.