Thanks to one and all for your positive comments.
The storm was quite active.
Lightning acted rather like a honking big strobe light, freezing any motion relative to the cloud, giving it a nice sharp outline.
I had witnessed another remarkably rare event out of Hong Kong on a different flight..blue jets (worth a Google) from the top of a very active storm!
Unfortunately I did not have a camera with me to record the remarkable sight and despite 20,000+ hours in my log book, never saw a similar display again.