One receives units through the tutorial and as a reward for some quests. Haven't encountered a quest where you can receive warriors, but that doesn't have to mean anything.
As for having 8! units of the same type rewarded (thus not needing any barracks) is new to me. Is it possible that you overlooked a warrior barracks? If you're absolutely convinced that this player is cheating, then I'd suggest you report that player by means of an in-game ticket.
Regards,
Bloodwyn