And no we don't call these a "dirty" line that's something someone made up for the purposes of the article. We call it "unattrib" and it's quite common, serving many useful legitimate purposes.
One thing that I find surprising about the Hegseth case is that most SecDef do not use the computer in their office it all. A couple recent ones still don't even have a computer in there. Normally staff handle 100% of communication and briefing outside of phone calls and video calls. He's clearly still adjusting to the reality of operating within the _confines_ of DoD headquarters.
Also the article's mention of using Wi-fi in the back of his office doesn't make sense to me, there isn't any Wi-fi available in the suite or anywhere nearby.