I'm not OP but it comes from the fact that Spectre is a very specific bug, but is colloquially used to refer to all speculative execution bugs found after as well. So its true that AMD is susceptible to Spectre; However, the mitigations have a much lower effect on performance. Additionally AMD is not susceptible to the multitude of additional speculative execution bugs found in the time since Spectre was first announced.
Spectre was used to refer to all speculative execution timing leaks from the very beginning. That's why they called it "Spectre" - because it's going to be hanging over us for a long time.
