Does Irresistible Fae Folk moving an enemy to a battlefield make the controller of the Irresistible Fae Folk the attacker or defender?

You are the attacker. The enemy unit becomes the defender.

When you move Irresistible Faefolk to an uncontrolled (empty) battlefield, you're the one who applies the Contested status to that battlefield. That makes you the attacker per Rule 459.2.b.1. When Faefolk's triggered ability later moves an enemy unit to that same battlefield, that unit arrives as the defender — moving a unit into a combat via an ability doesn't retroactively change who started it.