Or, as in many cases, the group finder reset itself and checked healer for him.
I've seen this happen many times on my Sorc and on my Merc. I can group find with only DPS checked for days. Then, all of a sudden, Healer will be checked for both of them. If I don't catch it, I'll end up joining a group as a healer.
ive had this happen to me too, jsut another screw up by bioware that they havent addresed.