Plex and data usage

Hello, this is all really Greek to me so please bear with me while I try to explain my setup

I am using Plex when in my motorhome using app.plex.tv/desktop . I access my Plex Media Server (I think that is what it is called) through my MiFi network to an external portable hard drive that is connected to a computer in my motorhome. I am on limited data and would like to confirm that I am not using data when watching any of my recorded media.

Sorry if this is not written correctly, I tried.