If your claim is that he doesn't believe Greta Thunberg specifically is the Antichrist, then sure. But that's just listening to the words that he says. He never says he believes Greta is actually the Antichrist.

However I believe he does actually believe what he actually said, which is not any more sane: "In our world, [the Antichrist] is far more likely [than Edward Teller] to be Greta Thunberg."

So yes OP is correct that Thiel said and does actually believe Greta "is potentially" the Antichrist. But that's a different claim than saying that she actually is the Antichrist. There are thousands or potentially millions of people (most unknown to Thiel) who could fit into the Greta-Antichrist category broadly. So it's a much weaker claim than that Greta is herself singularly the Antichrist.

Both claims are equal levels of insane and intellectually bankrupt though.