It's not hard to imagine if you remind yourself that you are talking about 18 - 22 year old kids. Also, "Full of themselves" is somewhat of a relative term. I doubt that he meant that they were "Full of themselves" to the point that they thought they could beat all comers. I think there's probably a fine line between a team like this developing confidence in themselves (which you want) and becoming "full of themselves" (which you don't want).