Does a defendant have a right to remain silent when confronted by a witness who claims to have purchased marijuana from him?

In People v. Cockrell (1965) 63 Cal.2d 659, for example, the defendant was arrested and confronted by a witness who claimed to have purchased marijuana from him. A police officer asked the defendant "what he had to say about 'that,'" and the defendant remained silent. (Id. at p. 669.) The court concluded that the defendant's silence was constitutionally protected regardless of the adoptive admissions rule because, "even though it does not appear that [the defendant] made any statement indicating that he was invoking his privilege against self-incrimination, he had a right to remain silent and an inference adverse to him may not be drawn from his silence." (Id. at p. 670.)