I completely agree. I've done a similar experiment on this rather young HN account and it was already able to deduce some things that I never explicitly stated. It probably doesn't require much more than a megabyte of someone's Slack messages or emails to build a profile on them, and there's much more data out there than that. People can be linked by their footprints in big tech products, or more crudely by techniques like stylometry, which is fully accessible to foreign governments. LLMs will likely enable even more aggressive techniques for linking people's public data, let alone to analyze it.