How many D1 runners participate in XC each year, who in HS ran 9:10 or faster? Must be a couple of hundred, right? As far as winning XC nationals, only the first 40 to 50 places "matter" in the hunt for the team title. So you could say that in any given year, a 9:10 or better guy has statistically maybe a one in 5 chance of being part of a national championship team (i.e., 40 or 50 out of a pool of a couple of hundred).
The point being, even if the entire first 50 places are composed of guys who ran 9:10 or faster, that doesn't imply that just because you ran 9:10 or faster, you will probably finish in the top 50, because the pool of 9:10 or faster guys is quite large.
Then consider that most of those 50 spots will be taken by guys who ran faster than "just" 9:10. Sure, good coaching will get some 9:10 guys to improve a good bit, but most 8:50 guys will also receive good coaching and are just as likely to improve.
There are seemingly many anecdotal stories of 9:10 or slower guys who over-achieved in college and were part of championship teams, but what are the odds that you will have 5 9:10 guys get, for example, places 11, 18, 22, 28, and 34, for a team score of 113, to win NCAAs in a year without a super-dominant team? Any one of those 5 places would be a huge achievement for a 9:10 runner. To have 5 guys on the same team do it in the same year is highly improbable.
Then add in the OP's stipulation (if I understood correctly) that these 5 basically WERE the entire XC team (i.e. it wasn't a team with 20 solid runners, of which these 5 rose to the top), the odds are extreme.