Ethernet on MacBook Air via Bluetooth Pan instead of Thunderbolt Bridge????

I have a MacBook Air Mid-2012 running macOS Catalina 10.15.7.

Ran an ethernet cable to my basement so my daughter can student teach from home. I wanted to get everything set up and working so my daughter could just plug-her MacBook Air Mid-2016 running.macOS Sierra in and be on her way. Her MacBook connects instantly via Thunderbolt Bridge with a Thunderbolt to Ethernet cable.

My older MacBook Air however connects using the Bluetooth PAN????? It works fine but I just don't get why? I've turned off my phone and the WiFi on the MacBook so my service is definitely coming thru the Ethernet cable. My Thunderbolt Bridge will not work like her's does or at least I don't know how to configure it to work.

Any suggestions?