This thread certainly implies it.
And there was a suggestion in that thread as to why it happens to some people and not others:
The preference may have been carried over from vBulletin, where I think I deliberately opted not to display whether I was online but you could still see past posts and threads.
So depending on a person’s profile preferences in vBulletin, it may have tried to reproduce those by hiding a person’s profile here on Discourse.