Omi really had two choices- drop the subject altogether, or admit a potential weakness to a potential enemy. While he didn't like either choice, one was obviously better avoided. Admitting ignorance just wasn't a possibility.

He looked away, out to the courtyard at large, and unconsciously shifted his shoulders in an attempt to settle them in a way that would stop pulling on the stitches in his back.

...Okay, maybe he was sulking just a tiny bit, but he wasn't about to admit that, either.