H1000,
Does the TIU really communicate directly with the App? The way I picture it is the WIU acts as a middle man between the App and the TIU, just as the TIU acts as a middle man for the DCS remote and the DCS engine on the track.
Yes, you are correct. Whenever a Refresh command is issued, the app polls the WIUs for connected TIUs. That's how the app gets "reacquainted" with the TIUs.