In summary the court said: The court opinion, by Chief Justice William Rehnquist, held that the due process clause protects against state action only. Police action was never mentioned or effected by that case.

Here is due process (5th Amendment): https://en.wikipedia.org/wiki/Due_Process_Clause

Due process protects individuals from intrusion by the state. In that vein the case effectively says state agents without policing authority are not obligated to intervene as police would against private citizens.