There's nothing wrong with a guy wanting single occupancy. At most other airlines it's the norm. when I was new at Eagle in '91 as a newbie, we got single occupancy as standard policy, and it never changed over there for new hires. They never had to double up, and they never had to pay for their own room.
This isn't undergrad college where you share a room. You are paid professionals and deserve to have your own room for training. I'm not sure how or why you folks can justify double occupancy and dress the guy down because he actually wants to be treated like an adult.