The Worthy
Ruby was sort of confused by Thor's reaction and didn't know exactly the cause. Being able to pick up Mjolnir was definitely not on her radar of being why Thor would react in such a way. A more likely reason was how she got over there. But he had been in the air like it was nothing so even that didn't make much sense. He clearly was aware of the Dreams and what they could lead to.
"How what? Getting over here? It's my semblance."
Yep. She was now confused. And they had a dragon to fight. Oh well, so holding Mjolnir to Thor so he could take it.
"This is yours, right? I could have sworn I saw you using it earlier."