@cyberminion
The SG2100: the default configuration all the ports labelled LAN are on the switch. If you don't do anything all the ports are on the LAN segment. The WAN is a distinct device; default mode is like a good old WRT54G: WAN goes to the Internet, all the LAN ports in the back are switched together. If you want to create a LAN and OPT1 (your original picture) you have to do explicit configuration to create VLANs and Tagging for the different ports on the Switch itself.
Unit with separate NICs. Hard to say, it may depend on how the separate NIC devices are connected. Easy to see them connected to an unmanaged switch, if there is no explicit configuration, I think again you wind up with the $5 unmanaged switch from the store.
I'm currently behind a SG2440 that has distinct NICs for WAN, LAN/OPT1/OPT2 and I am not going to break my configuration to test the theory :) ( wife would get annoyed at me )
Sometimes the switch devices let you have pullup/pulldown resistors on pins to force a configuration after power on. I don't have the Netgate schematics or the datasheets so can't say if anything like this is being done, but most switch devices I've used default to unmanaged mode after a power cycle.
If you have the serial console cable if it breaks you should be able to get to a shell and poke around. If I'm recalling correctly, basically look for a 0 byte config.xml and then look for a backup of config.xml that is non-zero length and simply copy that over to fix it.