Settle an argument on bandwidth and Netflow

We have a Managed Wan circuit which is provisioned at 10Mbps

I am also using Fluke Netflow tracker to monitor the traffic usage on this line.

Today the traffic is showing 13Mbps which I would say is the site is trying to move 13Mbps but the provider will be dropping 3Mbps of this.

Another colleague has the opinion that a 10Mbps line is 10Mpbs full duplex so 10Mbps each way.

So we have taken a second look at the Netflow and it is only showing 8Mbps in and 5 Mbps out. To which he says there will be no dropping of traffic.

Who is right?

Thanks

Roger