you know this looks bad, but all three monitors are still working fine, no busted screen, and the computer is still humming along since it's displaying stuff so really this person got really lucky.
the lesson is to buy a proper desk, not use some cheap planks of wood or whatever.
imo, they probably just used the triple monitor arm as is
no you can't do that, you have to spread the weight of the load, put a 2x4 under the mount to spread the load, b/c just clamping it to the end of a desk, that is probably plywood, will eventually warp and break.