I've used more than 300GB in a day on my home internet connection, it doesn't seem outrageous to me that someone could use 1/100th of that on a mobile connection per day.
Not the OP. My parents in India don't have wired broadband. They only use mobile data. So when we do a FaceTime call, they easily consume about 1 GB (give or take a few MB as I didn't do any scientific measurement) in less than an hour.