Seems like the author thinks that protecting yourself is exclusive to non-cis, non-white, non-male folks. I guess they've had a relatively rosy experience on Twitter thus far, which is a tad mind boggling!
Some of this is backed by studies I've read, and some of it is my own anecdotal experiences, so take it for what you will:
Sharing your identity on the internet is dangerous. Deliberate bad actors aside, there is a whole world of people out there with varying life experiences and tribal knowledge that they use to perceive the exact same world you perceive when you consume online content in a potentially different light than you do. Though you're looking at the same thing, because of the lens of your life experiences, two things that are exactly the same can be perceived two different ways by two different observers. Sometimes this does something innocuous like making someone engage in healthy debate with someone they otherwise wouldn't. In other cases it results in a lot of assumptions that the observer may make both directly and indirectly about you and what you said.
When you're out and about in the real world what stops an observer from making the very same assumptions that lead them to an outcome online is the lack of notion that they know you. An online profile, and things like pictures, establish in peoples minds the notion that they know you somehow (whether they'd like to admit it or not, their actions are influenced by this phenomenon). The author kind of touches on this phenomenon when they mention that profile picture changes can result in decreased engagement, but some studies have pointed out that it can indicate that your followers already have an unhealthy relationship with you and feel some autonomy over your life choices or at the very least your digital presence.
From here you're one tweet away from being someones virtual punching bag, subject of a mob, etc... all of these things are abusive but doubly so if someone can determine real world information about you and carry that poor outcome from the digital landscape to the real world landscape. My point is that all people, on any given day, are capable of abusive behavior and unfortunately it is still on you to protect yourself from them, whether they have a history with abuse or if they just had a bad day and you were the thousandth bee sting they've felt that day.
While insulating yourself from abuse online is doubly important for marginalized groups that suffer from a larger pool of deliberate bad actors than cisgender, white men we shouldn't ignore the fact that anonymity, and the concept of protecting yourself, is useful to everyone.