Is the statement true that naming body parts is not sinful, and that sinfulness lies in slandering reputations and speaking falsehoods? And does this mean that speaking of or mentioning the names of private parts is not forbidden?

The mentioned text belongs to Abdullah ibn Muslim ibn Qutaybah al-Dinawari in his book "Uyun al-Akhbar," and this statement is correct. Indeed, poets used to say such things, and a group of the Companions heard ghazal poetry and did not condemn it. What is prohibited is to express ghazal towards a specific person and to mention their physical charms.