Reading between the lines of the article it seems they "walked in" because they were brought in to be interrogated about their daughter. People are often unaware of their rights and importantly this wasn't about their activity but their daughter.
It's all well and good to have your own OPSEC tight, but anyone you communicate with can spill the beans, either by turning on you or if they don't have OPSEC as good as yours
https://netzpolitik.org/2026/messenger-ueberwachung-immer-mehr-polizei-ueberwacht-messenger-wie-whatsapp/
