I agree with most of the comments. I use chairs, but if they did, they would have been blown over and flattened by the weight & velocity of the concrete. I do agree that without plastic, the water from the mix would be partially absorbed by the sand, but it still weakens the mix. I would have edged to the slab with treated “ground hog forms”, drilled holes at 2’ centers (or whatever centers are on the prints) and place rebar tips in them. When I do a slab like that, I use chairs and then put a blob of concrete at each chair to proved more support before I let the driver turn it loose. Keeps the rebar up in the proper level. Low level Concrete contractors like to water down floors because they think it makes their work easier.
In a southern non frost climate, that concrete job will probably hold up to light use, but I’d be afraid of shrinkage cracks due to excess water. In my area, or should I say under my supervision, concrete would never be done that way.
