I think it might be because of how Someguy made him..
He'll randomly switch outfits at times, with the above post, it might be tricky, he might wear your armor, then switch to another set..
It seems like he'll switch to other armors, for instance like the quest where you go to the Vault 21 hotel, and he gives you a new set of clothing to go along with his..
And when he confronts you at the Mojave Outpost, and switches over to the NCR armor, and makes you equip it, to glue in some kind of speaker that plays music.