For wired Ethernet it depends on whether the traffic even reaches that port or not. Old dumb Ethernet hubs used to pass all traffic to all ports, but modern switches only send traffic to the intended destination.

It will show you everything coming out of the switch port but only traffic to/from the connected device will come out the switch port.

You have to use ARP poisoning or some other trick to get other network devices to send ethernet frames to your mac address in order for the switch to forward them out your port.