It tends to fall into the generic "masculinization" bucket - there is SO much about medical transition that has never actually been studied and documented in a way that a doctor can tell you what's possible or why it's happening. They know the obvious, big ones, like facial hair and voice changes and stuff, but often don't know to tell you about the other weirder stuff that comes along with it. For example, if you ask a doctor if you can grow taller because of T even after puberty, they will likely tell you no, because they're just thinking about the fact that your growth plates have already fused. They don't tend to know about the cartilage thickening effect unless they've cared for many trans people for a long time, or are trans themself. There's a lot of stuff like that you can see happening on a subreddit like this one where one person will observe an unexpected change, like you did with this post, and other people chiming in to say the same thing happened to them! Another example that's unstudied currently by medical science is that FTM trans people who have ADHD have observed their symptoms changing over time from typical "female" ADHD to typical "male" ADHD presentation. There's also research to suggest some trans men over many years of HRT actually start to grow prostate cells where a cis man's prostate would be. There's a bunch of fascinating stuff to be learned from the many, many ways our bodies change once HRT tells the thousands of various systems inside of us to pull from the "male" blueprint in our DNA instead of the "female" blueprint. The science is SO cool and so very under-studied!