Vpn client / traffic analyser

I noticed that the clients I have redirected through the openvpn client only have uploaded data and 0 downloaded when looking at traffic statistics for these devices.

Is that expected behaviour and if so what is the reason?

I am not using policy based routing, using a fw script executed when vpn comes up redirecting all traffic thru the client tun interface.

Presumably the tun interface is not measured? But how come there is upload data?

Cheers