Monitoring Network Traffic on a Switch.

Is it possible to monitor all network traffic on a switch on all ports with one sensor connected to one port, without mirroring ports?

There is company that claims they can monitor network traffic on all networks connected to a switch with one sensor occuppying one port. Basically, they claim this port can see all traffic destined for other ports.

My understanding of a switch is a port only sees the traffic that is destined for it. This company defies this rule with their claim.

I am relatively new to network security, so any comments are appreciated.

Thanks