The egg proteins are coagulated but dispersed in the colloidal solution. The motion brings them out of solution. You can try it at home by warming up some mayo in the microwave and then rubbing it between your hands: you'll get a stringy oily mess.
To play this discussion out further: it depends on the heat and it depends on the motion. I’ve made plenty of Hollandaise (which is a sibling of Mayonnaise) in the blender with “boiling” butter poured in, and it stays quite hot... especially when it continues to warm on the stove top.
If I microwaved it from cold, it would break almost instantly.
