They're exaggerating the problem. You can get a users IP and user-agent string, but only in a vacuum, not linked to your username or anything else. And even if you could, this wouldn't be mutch of a problem, because this information gets passed to basically everyone and doesn't reveal mutch(only strongly approximated location(next big city in the worst case) and what browser an operating system you're using). Comparing this to email tracking pixels is a misleading comparison, because these can be connected to a single person(the recipient of the email), making the information more valuable(and add another layer of information, such as the time the email was first opened).