My friend has Mystic Confluence and tried to target a token creature to be returned to the owner's hand. I have read that token creatures are considered creatures, but why would you be able to put a token creature into a hand since you can't necessarily spend mana to play it from your hand.
Token creatures are creatures, so they can be targeted and affected by anything that refers to "creature(s)". If a token is returned to a player's hand, it disappears, so it doesn't matter that they wouldn't be able to cast it. This is stated in rule 111.7:
A token that’s in a zone other than the battlefield ceases to exist. This is a state-based action; see rule 704. (Note that if a token changes zones, applicable triggered abilities will trigger before the token ceases to exist.)