for those who're curious, it's actually true.
your mobile phone is ALWAYS LISTENING and processing the surrounding audio.
however, this happens locally on your device and the conversation isn't parsed to understand what you're talking about. so, the phone only checks for specific words like "Hey Siri" and discards everything else.
If your phone is not always listening to you, then how does it know when I say "hey siri?" :)
This still haunts me