The objector was unaware of failure modes of materials. Mechanical engineers can confirm that in a surface experiencing strain tension, failure will occur at the weakest point. Once that failure occurs, the new weakest points are now the ends of that tiny initial rip. Because the ends of that first tiny rips are now the weakest points in the surface, those will be the places where the next failure will occur. (Think of what happens if your pants rip-- once that rip starts, it continues to grow longer.) The ends of that expanding tear will likely continue to be the weakest points for quite a while, assuming that the surface is relatively uniform in thickness and composition. The tear will continue to lengthen and grow until all the strain energy is released. This principle of failure holds true for most materials including rock and rubber.
You can watch a water balloon producing a linear crack as it bursts:
https://www.youtube.com/watch?v=NMbM-ERy2Lk
You can watch an air balloon burst with a linear crack as it bursts:
https://www.youtube.com/watch?v=5nGaXY5Gxy4
Additionally, pressure waves that are creating cracks travel 3 times faster in rock than they do in water. Thus, the crack in the earth's crust propagated much more quickly than the rate at which the pressure rate dropped in the subterranean (or surface) water. A water bottle is very small, so this difference in propagation rates is close to zero, whereas for the earth it is very large. A water bottle might burst in just one point, not with a crack, because there was no time for the crack to propagate due to the small size of the bottle. However, as these slo-mo videos show, the linear crack phenomenon can be seen even in a very large water balloon.
To hear a 30-minute radio program where a mechanical engineer discusses this objection, go to:
https://kgov.com/answers-hpt-oard-linear-crack