But some muppet passenger who was probably talking loudly, or reading his broadsheet all through the safety briefing because he/she's an oh so frequent traveller, decided they'd seen enough to panic, and opened a door.
Just how does a muppet on an aeroplane with no mid cabin underwing exits, open a door? Are you really suggesting the cabin crew just sat there and allowed that to happen?
As for evacuating on the starboard side, it's entirely possible and reasonable, that the tech crew on hearing an explosive sound shut the engines down and ordered an evacuation. In many airlines, it is up to the cabin crew to look out the door window, assess any visible impediment to opening the door (smoke, fire, water, obstruction) and if deemed clear, open the door and thus deploy the slide.
If the explosive sound was just a compressor stall, and there's no visible damage to the cowling in the photo at the start of the thread, then why not evacuate from the starboard side. Finally, at a guess, the CC probably wouldn't all agree on which side the explosive sound came from and would therefore rely on what they could see.