We have empirically verified the vulnerability of several Intel processors to Spectre attacks, including Ivy Bridge, aswell and Skylake based processors. We have also verified the attack’s applicability to AMD Ryzen CPUs. Finally, we have also successfully mounted Spectre attacks on several Samsung and Qualcomm processors (which use an ARM architecture) found in popular mobile phones.
So in other word, the researcher haven't tried it on AMD processors, but they think the attack would work. AMD, on the other hand, is saying the attack won't work.
Frankly, I believe in PoC||GTFO, so AMD is safe in my book for now.