They hacked the TV OS, then used the TV UI to do a web search with voice-input and observed (still on the UI!) that the voice input didn't stop immediately on silence but kept extending the search prompt with everything said [0].
The OS-hack was irrelevant for this, the whole sensationalism that a listening process is running (and therefore the device is listening to everything) is just drama added to the sober fact that someone started voice-input, the input field is still displayed on the bottom of the UI and keeps getting populated with new input.
There is an important message in this about security hardening, privacy, data protection, but this conspiracy theory that everything is made to spy on you is not helping...