You're wrong. They take units from the garrisons of the towns or castles they're in. And what are you even talking about, they do recruit from villages, ever wonder why theres so many missing troops in the recruitment screen?
I've looked at the coding, they spawn based on modules/sandbox/moduledata/paryTemplates.xml
The army they spawn with is defined under "kingdom_hero_party_kingdomenamehere_template
The aserai for example, use this template
<MBPartyTemplate id="kingdom_hero_party_aserai_template" >
<stacks>
<PartyTemplateStack min_value="16" max_value="16" troop="NPCCharacter.aserai_tribesman" />
<PartyTemplateStack min_value="8" max_value="8" troop="NPCCharacter.aserai_footman" />
<PartyTemplateStack min_value="8" max_value="8" troop="NPCCharacter.aserai_skirmisher" />
<PartyTemplateStack min_value="4" max_value="4" troop="NPCCharacter.aserai_tribal_horseman" />
<PartyTemplateStack min_value="2" max_value="2" troop="NPCCharacter.aserai_mameluke_regular" />
<PartyTemplateStack min_value="1" max_value="1" troop="NPCCharacter.aserai_mameluke_cavalry" />
<PartyTemplateStack min_value="4" max_value="4" troop="NPCCharacter.aserai_infantry" />
<PartyTemplateStack min_value="2" max_value="2" troop="NPCCharacter.aserai_veteran_infantry" />
<PartyTemplateStack min_value="5" max_value="4" troop="NPCCharacter.aserai_archer" />
<PartyTemplateStack min_value="1" max_value="1" troop="NPCCharacter.aserai_master_archer" />
</stacks>
</MBPartyTemplate>
Whenever a lord is released or escapes captivity, they instantly respawn with a base stack of this. They then will run around pulling units from garrisons, and recruiting units the same way the player does. If they are running around with an army of 1, hold alt and mouse over them, most likely they have 40+ wounded troops, and they've either gone bankrupt, or they've just escaped a major battle where they lost, but were not captured.
Unlike warband, troops barely heal when moving, so, an AI lord who has been defeated but escaped, is going to spend a very long time running around without an army, because it's entirely wounded. You have to stop moving on the overland map, and or rest in a settlement to get full healing. Also, most AI lords, have virtually no medicine skill, which further hampers their ability to recover wounded troops quickly.