Broadband data limit with mybooklive

I’ve just had hi speed broadband installed so bought a WD MyBookLive 3T. I got a message from by broadband provider that I have used 32Gb of my 40Gb limit this month. I have checked the usage and most of it is data upload. I can only think that this is when I updated a lot of video content to my MyBook over my internet connection at home.

Is this normal and should the MyBook not be on my internal wifi network not the external internet. Have I set it up wrong?

if you uploaded the videos over your internet connection, yes, it will use your data.

If you uploaded the videos using your LAN, no, it will not use you data cap from ISP.

Thanks. LAN from now on.