Here's an exercise for you: go through the list of US protected classes [1] and see which ones are explicitly stated and which ones aren't. It's actually enlightening. For example, I don't think I've ever seen ageism specifically called out.
As for the impact of the Indian caste system in US tech, I can't really comment on that. It's not my lived experience. I've worked with many Indians. No idea what their castes were. Saying that, just like racism I find it incredibly plausible that if you grew up in such a system, the effects are pervasive and linger.
So should Google allow such a talk? That's a difficult question. It's clearly a divisive issue. It reminds me of Meta telling employees to stop talking about abortion [2]. Now that issue probably doesn't lead to workplace discrimination (alleged or actual) although you might be able to argue that your political views could hurt you. There's something to be said to keeping your political views to yourself, particularly at work.
I imagine (but, again, don't know from experience) that this might be on the level of racial discrimination in the US workplace. So it seems worth examining. I imagine to mahy outsiders it might not look "real" because at the end of the day they're all Indians (which, to be clear, is also a form of racism).
Is a talk the best way to handle this? I honestly don't know. I can sympathize with avoiding divisive issues and also with the desire of a company to cover their ass and not create an HR nightmare. I really wonder if this ends in a lawsuit.
[1]: https://en.wikipedia.org/wiki/Protected_group#United_States
[2]: https://www.theverge.com/2022/5/19/23131714/meta-ban-abortio...