I think the reason some people might believe this claim is because we’re taught in school that the moon’s gravity causes the tides. I think the reasoning goes, “well if the moon’s gravity can affect the tides, surely it can affect smaller things too”
Maybe bacteria could be affected by the gravity
If the bacteria has a mass of 1 millionth the mass of a human, the gravitational effect the moon has on it, would similarly be 1 millionth the effect it has on a human.
Stupid physics. 🙄