You're correct, although I still get the parent poster's point.

You weren't anonymous on SA in the sense that law enforcement couldn't find out who you were, or whatever, unless you used a burner credit card and... never used your own wifi, or whatever.

But you were anonymous in the "Google search results" sense that nobody was expected to publicly share their real names or faces, and what you posted on SA and its ilk didn't necessarily follow you around for the rest of your life.