I'm curious as to how you managed to

Also, when I booked the flight, it gave me a choice of seats and I chose some random seat near the front. Can't seem to find any reference to this in my booking and it seems that it's just "first come first served" so why did I get to choose a seat in the first place?

pull that off. I can't even think of a step where you might have confused it for a seat selection.