Should a Freezing Trap return a stolen minion to my hand?

Solution 1:

Nope, once mind controlled the minion is owned by the opposing player. It is working as intended.

Solution 2:

Ownership is transferred when a minion is mind controlled. Ownership in Hearthstone is based upon whoever holds the minion on their side of the board. As soon as a minion is on the opponent’s board, they own it. In this instance the priest you fought had the hyena return to his hand with an increase mana cost of +2 to the card’s actual mana cost because of the freezing trap.

Depending on the situation this is a risky but clever play in order to trigger your trap so that his already in play minions are not returned/sniped with an added bonus of taking away a minion of yours.

Even in instances where mind control is temporary; whoever holds the card is the owner on that specific turn. Example: A priest obtains cards from a rogue using their class special cards and gets a Shadowstep. He uses the minion/card that only temporarily mind controls a minion and uses Shadowstep. The card would return the minion to his hand and not the “original owner” because the priest is the current owner at the time.