Almost certainly BS.
I’m querying the blog every 15 minutes, so if it had been updated with a post about GPT-4.5-Turbo, I very likely would have caught it.
I suppose it is possible it went up, Google scraped it before they took it down, but I missed it, I just don’t think it’s real.
Besides, everything I’ve seen speculating about an intermediary model before GPT-5 has referenced GPT-4.2.