If you look one page back, you will see that it says "Fred *AND* George Weasly." they were both sitting there... George COULD'VE been asleep right before Fred nodded off; therefore, this is NO mistake.
Unfortunately, it seems that with the American editions of these books, there happen to be many mistakes. This is common when a book is summerised first and then re-written. It IS true that most of the team were falling asleep, and also that Fred AND George Weasley were both "nodding off".