I think he was saying the antichrist would be more likely to be a person like Greta, not Greta herself, but the clip cuts off the context at the beginning so it is hard to say.
https://www.nytimes.com/2025/06/26/opinion/peter-thiel-antic... - Gift link
https://archive.is/mPjPq - Archive link
So yes, he does say it's more likely to be Greta Thunberg than an "evil tech genius", but does not outright say she's the Antichrist.
I still find it strange that he's afraid of her creating a one world government.