The point is that it does NOT take up population in a sense that it does not count to the ingame population limits. If you'd count it as population you'd have to increase the population limit in the graphic as well (5/17 or 5/202), only as long as the horses live though, which would be even more counter-intuitive.Thanks.
Certainly counter-intuitive and created confusion for casters on a couple of occasions.
If it's within CaptureAge's ability, I'd suggest a complete reversal of the current situation; horse/camel lacks ability to attack - so not military, but is a unit that performs a function (scouting) - so takes up population.
p.s. great job by the whole team - well done.