I do wonder why they only listed the one AMD CPU. The text in that area of the actual article explains what is going on and how it's Architecture based. So either they simply didn't test Ryzen and it could be affected or... they didn't bother because based on the research they already knew what the outcome would be.
They certainly are showing how through the various Intel families they all have this "leakage". I might have missed it, but since I didn't see any definitive statement about not testing more ARM/AMD chips... it does make me wonder. So I can only ponder that the way ARM/AMD does certain things didn't really change or... they just didn't test more cpu's for reasons unknown.