Saw this in the article:
This is the biggest drawback of hidden SSIDs. When a network is hidden, your phone or laptop has to constantly shout, "Are you there, [Hidden Home Network]?" everywhere you go.
There is a paper that describes how an iOS device listens to everyone else’s phones as they broadcast all the SSIDs they connect to (regardless of where the two phones intersect). It gave the impression that phones also reveal non-hidden SSIDs when looking to connect, as it’s uncommon for people to have hidden SSIDs.