Would you mind saying what you mean by 'lurking'? In all my life on the Internet, it's a positive thing when joining a community. You're invisible to everyone and just read. Why should people not do this? It seems harmless to be in read-only mode.
In the sense used here, "Lurking into someone's thread" means sending an unsolicited comment to a thread you were not an expected participant on.
This is something we're broadly supportive of but which, if done poorly, can be socially contentious. You could imagine pathologically bad examples like "Hey thanks for working on this project for the last 8 months, but before you ship it, just wondered if we had considered adding a teal bikeshed? Taking the liberty of CCing seven people for their thoughts on the bikeshed you'll be building."
I noticed that in both places they use the term, they say "lurk in", almost as if it's a term with an accepted meaning within Stripe.
The fact that they say "read to your heart's content" also suggests that they aren't using "lurk" in it's usual meaning (which to me is reading but not commenting).
Stripe has a very specific culture of email transparency that they've posted about before, and they've likely developed company-specific jargon around it: https://stripe.com/blog/scaling-email-transparency
I've seen the opposite by senior management called the "swoop and poop". They haven't followed the thread at all, but they will swoop into a meeting without any context and poop all over the ideas because they are missing the context around the complexity of the problems.
I'd sooner have a lurker that read all of the conversation speak up than the opposite.