>>281747717
In this case, 人 is used as a "counter", specifically the one for groups of people.
Only certain things can be counted directly, while everything else needs an appropriate auxiliary counter. So 男の10人 is indeed "10 men", while 10男 would be incorrect.
Sadly, many other counters are kind of retarded. See
https://en.wikipedia.org/wiki/Japanese_counter_word#Common_counters_by_category for examples.
