Looking at some satellite data and their most likely flight-path it seems they passed close to (or through) a Cb that was growing incredibly fast: In the space of 15 minutes the top of the Cb went from around FL295 to FL410. Unfortunately it would have been that 15 minutes that they flew near it, so it'll be interesting to see what role, if any, that played. It's one of the fastest growing (and shortest lived) storms I've seen there.
Based on past experience it also seems to be the type of Cb that produces ICI, but I can't understand how that alone would cause an accident as, in the space of about 5nm, the cloud totally disappears and the crew would've been in VMC again. They managed to continue for another 60nm or so, all in decent visibility. Is the Cb just a conicidence or did it have some effect?
In short: Haven't a clue, it's puzzling.