If you add settlers while your max population is already reached it gives a notification.
'Maximum capacity reached. You cannot add more Settlers to your storehouse. Upgrade your storehouse to increase your storage.'
For new players this could be confusing since it is implying a bigger storage = bigger population. The text should be changed too:
'Maximum capacity reached. You cannot add more Settlers to your population. Upgrade or build residences for them too reside in to increase your maximum population limit.