My family had bought MiBox probably 3 months ago and use it to watch youtube/netflix/amazon prime and I have never used MiBox by connecting with my device simply because I don't watch anything on TV and prefer watching stuff on my laptop. I generally use VPN for day-to-day surfing and out-of-the-blue I saw ads in Dutch language on the MiBox when I was connected to Netherlands IP address even though my device was not connected with the MiBox. That raised some serious eye brows because my family members don't use VPN (yes, I asked them this question after finding the Dutch ad), so does that mean MiBox can track my device too?
The MiBox itself is not tracking your "device", but if both MiBox and the other "device" are connected via the same Google Account, they are definitely sharing the same Advertising ID, yes.