He should just be grateful that Qantas doesn't take the Scoot approach.

On Scoot if you can't fit in a single seat (determined by staff) then you're required to purchase a 2nd seat next to you (or upgrade to Scoot Biz - bigger seat). Ideally this is meant to be done at time of booking but can be done if seats are still available at check in. If no spare seats are available at check in then sorry... you can't fly.