In his post on Medium, Braun describes that he wanted to have a smart mirror for his mirror, just like one has a smartphone or a smart watch.
He says that he could not find one in the market (obviously!) so he decided to make one. He got the raw supplies and crafts, a switch board and a display from the market. He used a two way mirror for this.
With the a bit of experimenting, he says, he was able to create a smart mirror that sits on the door to the medicine cabinet showing him the weather, time, date, news and reminders, using Android APIs.