Instead of the aircraft type, engine type, etc, IMHO, the most likely reason was the decisions made by the MH crew vs the SQ crew.
Some crew fly a fine line close to weather, some give it a larger berth, and some crew attempt to go through it!
As S.I. said
When I met him later he added that he was as pleased as anyone for the diversion and had not looked forward to the ride through the storm.
I've flown with captains who have had passengers and flight attendants injured in weather related turbulence. Years later, they're still affected by this and they give storms a larger margin than other captains.