What he is testing is exactly what a column of water would do in a standard test. Re-watch the beginning and he talked about how to test it without the pump they would need at least a 92 foot long pipe. That would be 1,104 cubic inches of water, or 4.8 gallons of water, or about 40 lb, which would be 40 psi in the standard test. He is simply replicating the industry standard test that the manufacturers claim. You could argue that the test is flawed but literally every manufacturer uses it and I guarantee that 40 lb pushing down on a 1” by 1” square of fabric will stretch it.
In a standard test machine you clamp the material in such a a way as to not introduce deformities in the fabric.
I.e. the whole piece should start out flat, his test setup has it clamped around the end of a pipe. You can see in the video how some of the leaks and tears start at the stress points where the fabric is folded near the opening of the pipe.
It's meaningless to make any general assumptions about how such a non-standard test setup relates to how a fabric would perform in the standard test.
