I thought this would be more about stylometry but it's mostly about users literally posting the same identifiable information across multiple services, including in one example their age, dog name, profession.

It's all classic dox profiling techniques. Even the things like spelling differences being regional signals and commonality to specific things being discussed.

It's why one has to think about what is being posted to which community if using different identities, rather than posting the same things across all of them. Though any such effort would be a waste if reliant on some non-public info that later was exposed in a database breach which tied together previously unrelated profiles.