If I remember correctly there was a very active line of thunderstorms that crossed the territory from north to south on the evening of 5th Aug.
I don't know this particular trail but is it subject to flash floods? I have seen these in the Sai Kung country park and they can turn a small stream into a raging torrent in a matter of minutes.
From what I saw over the airport there was a lot of lightning associated with this particular goup of cells. Not a good time to be caught out in the open.