I'm my experience it is not possible to simultaneously launch 35 gliders with 3 tugs. So there should not have been 35 gliders on the strip.
If it where a competition I image that many of the gliders where open class with water on. These need to take off from the center of the strip. With 3 tugs the worst case is 3 gliders on the strip at the same time. Standard class gliders usually do not need to be on the strip at all to take off. They can be launched from the side by the tug pulling them onto the strip.
It is the ground crew's (and, ultimately, the CFI's) resposibility that there are no more gliders on the strip than necessary, and, in any event, no more than they can clear off the strip quickly.