If Momo does something to Greenbull, that doesn't mean that he defeated him. We've seen similar things happen with other characters, like Ceasar Clown knocking Luffy off because of his unique ability. Greenbull is made out of wood, and Momo can allegedly use fire, so Greenbull might get damaged and thrown away off of Wano, but that doesn't mean Momo took him down though.