Bull crap...if that was true, rain would be lethal. When water is dropped from a plane, it disperses as it falls. If it didn't, it would crush everything it's dropped on...such as firefighters and houses.
The physics is still valid, even though I haven't taught Physics in college since 1992. Rain drops are isolated bodies of water which reach what is called the "maximum terminal velocity", where the upward drag force of the air equals the downward force on the drop due to the pull of gravity. Small raindrops (radius < 1 mm) are spherical; larger ones assume a shape more like that of a hamburger bun. When they get larger than a radius of about 4.5 mm they rapidly become distorted into a shape rather like a parachute with a tube of water around the base --- and then they break up into smaller drops. The terminal velocity is between 9 and 15 meters per second, an average of 30 ft/sec or 20 mph.
When the drop hits the person it rebounds into itself, the front end meeting the back end, which results in part of the drop dispersing horizontally, just like a bug on a windshield. The kinetic energy of the raindrop is eventually converted into heat, raising the temperature of the skin of the person struck and the temperature of the dispersed particles of raindrop.
When a block of several tons of water strike a person standing below, the water impacting the person's head cannot reflect back into the block because the small mass reflecting off the person's head cannot move the mass of water behind it backwards or to the side. If the water falls over 100 feet it's the same as a person jumping from over 100 ft into water. In both circumstances the water is, effectively, as hard as concrete. The water becomes the windshield, the person becomes the bug.
