Corellation is indeed not causation and humans are good at finding patterns where there are none. He might also drink a strawberry milkshake each monday, or pray to the arcane, binary gods before going to work.

However it is okay if someone says: "Writing helped me as a developer. It might be different for you."

Hopping that easily from "works for me" to "must work for everybody else" without a second thought is indeed not reassuring coming from a software engineer where "works for me" is not enough.