Not always true. My landlord recently had a contractor call me. I did my usual "pick up and don't say anything" routine for unrecognized numbers, and the contractor silently hung up and never called back. Thankfully my roommate actually answered the call, but pick-up-shut-up prevents legit people from leaving voicemails and sometimes prevents legit people from reaching you entirely.

Personally, I would utter a confused "hello?" if I was calling somone, the ringing stopped, and no one said anything, but I guess not everyone would.