I don't remember all the details but regardless of that, isn't it still a good idea to check mirrors just in case?
Yes, of course the driver should have looked (and not just using the mirror as there's the blind spot to consider!).
I am not sure why you suddenly dismiss everything else. The driver in lane 2 was every bit at fault too, perhaps more so, as it put the car driver in lane 3 in danger by potentially hitting a vehicle that shouldn't have been there.
Putting yourself in the blind spot is stupid as you should drive defensively, and at this moment in time, you're now solely reliant on them not making a mistake. This is why I used to hate overtaking lorries that were left hand drive, as I felt vulnerable, so often floored it to pass quickly - while also checking that I could possibly move out one more lane in an emergency.
I prefer to drive with anticipation of everything someone could possibly do that would affect me and my passengers. Clearly there are limits to what you can do to predict the unexpected, like a blow out from a lorry you've just started to overtake, or hitting a wall of smoke, or debris around a corner etc, but it's good advice nonetheless.