Willbreaker and Chaotic Transformation

[wide plaza]

Hello, I have [[Willbreaker]] in play and I cast [[Chaotic Transformation]] on a opponent's creature.
I gain control of that creature before the spell resolves due to the willbreaker effect.
But why the opponent is the one who put a new creature in play ?

[serene stirrup]

https://scryfall.com/card/ori/84/willbreaker

Willbreaker <:mana3:292901508771610624><:manau:292901508754702338><:manau:292901508754702338>

Creature — Human Wizard
Whenever a creature an opponent controls becomes the target of a spell or ability you control, gain control of that creature for as long as you control this creature.
"Master your mind, or I shall master it for you."
2/3