Wonder if it trys to connect through the LAN (NIC)
It will try to connect if it thinks there's a net connection out there, but it should just time out when it realises that it can't contact the server. I think that part depends on how Windows is configured.

My suggestion would be to unplug the network, start Steam in offline mode, and then connect the network again. You should be able to disable the NIC instead of physically unplugging it, if that's an issue.