They had already taken the trailer off the hitch and it was sitting on the front caster wheel.

NEVER jack up a trailer if the front dolly wheel can roll/caster. If you're going to jack up the trailer while it's off the vehicle's tow hitch, at least straighten the dolly wheel (parallel with the main tires) and then lower it all the way until it locks out the castering feature (most Al-Ko gear I've seen allows this). Then chock/block the main wheel that will remain on the ground. If you plan to jack up both wheels at the same time, however, put the trailer on the vehicle's tow hitch first.

Chip Bearden