That was my emphasis as well. There are all sorts of internal internal-psychological/perceived-sociological reasons someone may go silent when in the presence

That was my emphasis as well. There are all sorts of internal internal-psychological/perceived-sociological reasons someone may go silent when in the presence of seemingly friendly authority (if one comes from an authoritarian household or religious background) that suddenly appears to turn on you. The layman who hasn't had a brush with adversarial police investigation techniques and doesn't have an explanation for a (seemingly) factual assertion by the police may simply not know how to respond, knows he needs to tread carefully lest something get pinned on him, but is unaware that silence is not considered careful at this moment (since, if he remembers, he is talking to the police without being cautioned or under custody).