I actually thought about that when I was writing it. Akira was kicked out when he was in his first year of HS, so "two years ago" would be right, but I felt that Rokoru would say "a couple" instead. To me, "a couple" means 2 or 3, and given the fact that they're third years, I figured it would make sense in context.

Unless I'm completely wrong and Akira was kicked out in his second year and not first.