I think so too unless whatever it is got completely covered in coralline then it is something in the coralline family it is just too firm and I heard it make a snapping sound when I broke off one of the twigsI think it’s more in the family of a coralline algae. I also think it has a different red macroalgae growing on the inside of the bunch where it was protected from herbivores.
I have never seen coralline grow on my red macros. It does grow on some of my greens that have more of a calcium base like mermaids fan.