"Don't get meek on me now, Diana." Thor said as she challenged him again. "It takes more than a single lucky shot to best me."
In his mind, that had to be what it was. She'd gotten lucky. It wasn't that she looked at him often enough and in such detail as to pick out flaws in his movements, then exploit them. No way that was it. Nope. Uh uh. He didn't trust himself enough to think that, but he did trust himself enough to come back at her. Thor had a plan, but it required getting Diana closer and having a solid object at his back.
So he did the only thing he could do there, seeing that playful sparkle in Diana's eyes and guessing at her next move: He planted himself like just another tree and he waited.