From the second picture it looks like there are two levels, so this could carry five cars two on the bottom and three on the top, and he had three all loaded on the top level. That would seem to be pretty top heavy for a pickup truck to pull if all three were loaded on top and the lower tracks were empty. 5 x 3500 lb cars is about +/-18,000 plus the triple axle trailer, so it is a big load but within the range for a newer 350/450 class pickup. From the first picture you can see the truck was a dualie.
You would have gotten a better view than the pictures show I would guess. Was it actually a double decker? I have never actually seen a 5 car trailer for a pickup, I am just looking at the picture and there seems to be a lower deck.
EDIT**** - Oops, I didn't read far enough. A bunch of others already commented on this.