Normally yes but depending on how the crank throws are arranged it is possible to get multiple different firing orders. 1,5,3,6,2,4 is the most common though. I'm not sure why this one is different.

I'm not a mechanical engineer so take this with a grain of salt but in the animation they show three different injections. The first is called the pilot injection and it serves to help make the start of the combustion smoother because there's already fuel spreading out in the chamber by the time the second, or main, injection event happens which delivers most of the fuel. The last injection even serves to keep the cylinder pressures high by ensuring the combustion lasts longer. This means that the pressure is higher later in the stroke which is when the connecting rod and crankshaft are arranged in a way that allows for better leverage and thus more torque. By using these three smaller injections compared to one larger one they get more work out of each unit of fuel. I hope this explanation made some sense to you and like I said, I'm no engineer so I might not be 100% accurate.