Seeing that it works for a ESP32 chip I would say that its very likely to work on a smartphones's wifi chip though the article didn't say. Many people carry phones with them everywhere and all the time. You could build a very impressive profile of a person. It could be used to see when they get excited, scared, angry, etc at depending on what they view on the phone, the phone call they received, where they physically located on the earth, who they are around (by looking at identities of other phones near them) and properly other things as well I have not thought of.