I had the exact same situation happen to me on Jan 1, 2014. I was moving a 10gb file from my wife's Mac Book to my Mac Book via the wireless network. Then I got a Data alert. That 10GB file was counted as using Verizons data. As anyone with small amount of networking experience knows, this is an internal network transfer. Verizon is charging for bandwith that is not being used. I spoke to a customer service rep right after it happened and they said they would have the tech team look at it. They never got back to me. I called again today and was connected to a tech named Veronica. She said that it does not matter if the transfer was internal or came from the internet, they dont have a way to differentiate between the two so they just bill you for everything.
If anyone from Verizon reads this, you may want to kick it over the legal dept. because you are opening yourself up for Class Action. That 10GB transfer cost me $100 in overages and Verizon WILL NOT ISSUE A CREDIT. It is the same as having 2 Verizon phones in your home but getting billed for talking to the person next to you. In no way does the transfer draw from the Verizon network, its a simple internal network transfer.