No, it's not symbolic, just the opposite, it's Orwellian newspeak/totalitarianism.
By your very own words: ""diverse" is just an HR term of art that means "black, Hispanic, or female"", i.e. a completely subjective, odd, and contextual local moralism.
The problem is that these folks believe that any 'questioning' of their methods or approach are in fact 'questioning' of the underlying positive impetus of their motivation (i.e. we all agree 'not being racist' is good, but that doesn't mean we have to buy into any specific moralisms about diversity).
But anyone who asks that kind of question in an interview is either a clown or a pill-swallowing victim, and it's definitely a massive 'Red Flag' in that you're entering into a dystopian social nightmare where you'll need special help 'interpreting' thew Newspeak.
People from outside the West are already having enough trouble keeping up with the basic PC stuff, this is getting ridiculous.
It's a sign of social decay, and that SF has 'peaked' in terms of it's relative importance. Thanks to COVID, the rise of China, Trumpian foreign policy which has engendered a lot of mistrust, the 'decentralization' has begun in earnest.
I work with developers in E. Europe and 20 years ago they would have jumped at the chance to move to the US, now they have a strong preference for staying home - the only motivation is money, but since there's massive Purchase Power differential, even their low salaries offer them fairly high standard of living - and their economies are growing consistently 4-7%/year.
The story really is not about 'people leaving SF' - it's about 'The End of Short-lived SF Mecca'.
Note that SF proper was not a 'centre' of anything really until about 2010: Google, FB etc. are all 'Valley'companies, not until the rise of Twitter, Salesforce, Stripe did we see 'SF Values' come to start to infiltrate the definition of 'Silicon Valley'. The Bay will remain important, possibly even the 'most' important, but much like broad relative US decline (i.e. 40% of global GDP in 1960, 25% today), the relative influence will wane. The 2010's were 'peak SF'.
Edit: I should add - a regular from outside the Angloshpere upon hearing the question 'what have you done to support diversity' would basically be baffled and probably have no real idea what the interviewer was asking. I don't think many Americans in these situations realize how hyper-American (at very least Anglo/American or Western) these kinds of things are. Imagine asking that question of someone from Hong Kong, Delhi, or god forbid the true capital of 'complicated diversity', Lebanon.