Fact-Checking this Viral Bottle Trick

A bullet traveling through water doesn't leave just an area of low pressure behind it—it leaves a vacuum, since the water cannot move fast enough to fill it. Yes, this is rapidly filled with water vapor, but i think it is a little bit misleading to equate the complete displacement of the water in the bore of the bullet's travel with the process that allows the water to change phase at low pressure, leading to the formation of voids. The void isn't forming because of low pressure; it's forming because a solid object pushed the water aside as it traveled through. You are, i think, reversing cause and effect.

5:27 "So cavitation bubbles were slowing down the propellers." Is this what you actually mean? You haven't explained why cavitation would alter the speed of the propellers; it lowers the speed of the vessel because the compressibility of a gas (or vacuum) yields less hydraulic force.