I haven't trolled through all the comments, so I'm probably repeating what's already been said. Firstly, as an ex-EK 777 driver, may I offer an enormous 'well done' to the cabin crew. Convincing pax, (is it politically incorrect to say 'particularly from that part of the world'?) to leave their hand baggage behind is impossible. Ethiopian Airlines had an evacuation in Dubai some years ago and most of the pax were Nigerians on their way to Dubai to do major shopping/business. There was NO way they were going to leave their hand baggage behind, and the crew wisely recognised this and got everyone off, with their bags, far faster than they would have if they'd tried to enforce the no bags rule.
I'd be very surprised if the final report on this incident doesn't come to a similar conclusion. If there were only four injured in the evacuation, I'd have to say I'm amazed. Given the wide age and state of health range usually found on any EK flight, (on average, every EK flight in my day was met by 10 to 20 wheelchairs, but maybe we should not go there right now as to why that was so), I would have half expected one or more deaths due to heart attacks and the like in the most benign of evacuations, which this was was definitely not.