That's not at all what the board's block diagram [0] depicts, but apparently they don't care to make that accurate. While the photographs do make it clear that there are three Ethernet ports, it's wrong to say that there are three Ethernet interfaces; the SoC only supports two and it's misleading to count the extra switched ports as extra interfaces because they do not even have the theoretical possibility of contributing to better routing capabilities.

[0] http://espressobin.net/wp-content/uploads/2017/01/ESPRESSObi...