The van might have been glimpsed at a distance, but if so it would have only been a moment and there were other things needing to be watched. A center-mounted cam is best overall, but yeah- sometimes it will 'see' what you can't, and the recording will be misleading as to what was visible. Still it seems you were prepared for something possibly being on the other side of the pick-up; good job that
I watch too many car-crash videos and many crashes are because of a vehicle lurking unseen behind a larger obstacle. Always remember that if you can't see then you don't know, and if you don't know then you drive accordingly
I like having a secondary cam mounted high at the driver's side edge to better show what I can see from my seat.
Decades ago on a bright summer day with open fields all around I approached a "T" intersection and stopped. The main road to my left was gently curved, as was my road which intersected at an angle too. I had looked left and right several times and looked again once stopped. Seeing nothing I started off gently. Just as I did I saw something at the edge of the "A" pillar and moved my head to get a better look at it. I slam on the brakes just as my van nose went into the near lane; what I'd seen was a full-sized black touring bike
The combination of our speeds and the road curves had completely hidden him behind my "A" pillar for a good 10 seconds. I'm sure he thought I'd seen him- I expected him to turn around and run me down to fight for intentionally pulling out in front of him because that's what it would have looked like to him. Luckily he didn't
Since then I don't pull out without looking around my "A" pillar by moving my head sideways and not just rotating it. It takes a lot less to hide something from view than most folks realize and we've got to watch out for that.
Phil