No, of course not the MAC. Just as an example nmap can guess the OS based on fingerprinted behaviours. There are pentesttools that can guess the OS.

Like i said. Old days. You could get access to a distribution switch where the physical security was all that mattered. The town where i grew up had some early variation of cg-nat that meant all devices where in a way on the same network. It created plenty of issues when trying to play online with friends during Quake/WC3 etc.