After looking over the OnePieceChapters scans for Drake's and Zoro's two clashes, I wasn't entirely convinced that Zoro hadn't used Enma, specifically in that FIRST clash because in the second clash which is what you're highlighting, Enma is very obviously sheathed, so I wanted to wait for the official scans for a clearer image of the first clash. One sword is clearly Sandai yet the other was unclear.
The official scans prove that Zoro
did Enma initially which is very cool.