The dialog he got when he plugged it in mentioned FTDI and "Vinculum" which appears to be a programmable USB interface chip with serial and SPI support
https://ftdichip.com/products/vnc1l-1a/ https://ftdichip.com/software-examples/vinculum-projects/Since it's not just a generic non-programmable serial chip I assume it's also doing something more. But it doesn't do Ethernet so I bet it's not actually PoE but like... power+serial over Cat5