It's clearly intended to be funny, but the reasoning is perfectly sound. If a particular kind of dark matter candidate existed, it would need to be distributed

It's clearly intended to be funny, but the reasoning is perfectly sound. If a particular kind of dark matter candidate existed, it would need to be distributed with a density that would result in occasional very obvious, very fatal collisions with people. Since we have no record of people dying due to inexplicably having large columns vaporized through their bodies, we can exclude this particular class of dark matter candidate particles. The more serious component of the research focused on searching for these events in old deposits of granite.