I am 80% sure that both groups have adult males and 100% sure that both have females as there are infants in both groups.
I think they were originally split into single sex groups at one stage because of some fighting. Over time they may have re-organised them so they now have the two breeding groups. They have been very successful with them breeding-wise but maybe its time now to give up their 'only Bonobos in the UK' title.