nope! you can tell nobody was at the slide in the first place, because if it was operating, people would be lined up on the stairs seen in he footage. if you look at another angle as well, it appears that the truck was empty and rolled down the hill on its own, due to the door being wide open.
the angle i have cuts off before it shoots off the cliff, but here it is:
and here's a slowed down version (0.25x speed):
i realized the stairs are separate from the slide it hit, but from what i can see, each slide seen in the footage appears to have their barriers down. so, it's likely it happened before the park/area was opened to the public. there also appears to be what i believe is a security member or an employee for a few moments in the bottom right corner. there is also another angle right near the front of the slide that was hit that shows absolutely no one was up there at the time. i don't think the water is on either, but i can't tell.
