「日本人は自分の家族のことを誰かに話す時、あまりいいことを言わない傾向がある」

Maybe this is more of a culture question instead of a language one, but I came across the above sentence in a textbook I'm studying from. Is it true that Japanese people don't say nice things about their family? Or does it have the meaning of "They don't flex about their family" or something ?

(PS. not sure what flare to use)