Well spotted and captured. We shouldn't take all warblers or little brown jobs for granted.
Amazingly I was in the same place this year (but 1 day later, July 13th) and I saw the same species again in the exact same patch of grass..........
Great shot - the only ones I've seen were running through long grass like mice, they are passage migrants here in HK.
It's true, it'sreally weird to see them walking around on the floor like they do.