I would say yes.

You think they were sitting on a release waiting for the right marketing moment?

Yes?

I have seen enough OpenAI and Anthropic carefuly timed marketing plays to expect it.

I would never announce GLM 5.2 in the same day as Fable or Apple's WWDC, for example.

I think it's a possibility, because labs trying to one-up each other is a fairly common phenomenon at this point. Previous Opus releases were immediately followed by GPT releases, for example. At some point the timing stops being a mere coincidence.