It seems like a typo or mistake. It is a little complicated to explain, however, because division can be determined by EITHER number on team OR by number of males.
My quick attempt:
If there is at least 1 male on your senior 5 team, two factors may determine division for coed senior 5 teams - number of total athletes on the floor and/or number of males. Teams shall compete in the largest division they qualify for by either standard.
Total athletes:
XSmall: 5-14
Small: 15-20
Medium: 21-30
Large: 31-38
Males
XSmall: 1-2
Small: 3-5
Medium: 6-8
Large: 9-18
A team of (10 males, 0 females) would be
large coed, as would (1 male, 37 females)
You would also need to define what is going to count as "male".