Sadachar means ancient custom, good or bad, not righteous conduct.

Evidence

But what is the meaning of sadachar? If anyone were to suppose that sadachar means right or good acts—i.e., acts of good and righteous men—he would find himself greatly mistaken. Sadachar does not mean good acts or acts of good men. It means ancient custom, good or bad. — Ambedkar, B R, Annihilation of Caste_ The Annotated…, 989

Categorization

• DEFINE: A crucial definitional correction — the third Manu sanction turns out to be mere custom.
• corroborated: 2 independent passages support this claim — Ambedkar, B R, Annihilation of Caste_ The Annotated…, 989