I'm happy Roy is a bonus char because both of my accounts have him at 5*,holding off sacrificing him for TA3 has paid off, good thing he gets TA3 at 4* so you feel that it would be really wasteful if you sacrifice a 5* but what's more intriguing is that he seems to be the first to return as a bonus char (after the very first season) if I'm not wrong.
There are still tons of units that haven't become arena bonus chars yet but at the same time someone is already becoming one for the second time. You've got to wonder what's in IS's mind; are those two slots really random?
The arena bonus char composition has always been (besides the very first season when we have 2 prevailing mainline banners, and a few season before the OG lord rotation became a thing):
4 or 6 newly introduced banner character + 2 "random" existing non-daily HB characters + 1 GHB character + 1 FE:H original character + 0 or 2 daily HB characters. When the new mainline banner has 6 characters, they take up the 2 slots that are normally meant for daily HB characters, e.g. the blazing blade banner season bonus char set consists of the 6 banner characters (Ninian, Karel, Priscilla, Jaffar, Rebecca, Lucius), 2 non-daily HB characters (Azama, Fir), 1 GHB character (Ursula), and 1 FE:H original character (Anna). No daily HB characters in this case.
The 2 non-daily HB slots have always been a thing, but Roy among all these potential characters in a big pool getting a slot this time is still pretty weird.