Nope. You're thinking of UPnP (Universal Plug and Pray) which does exactly that. That's a real security risk, but is oh so convenient that it's difficult to resist. It also is required for some devices that only autoconfigure with UPnP.
What I was talking about above is the inconvenient detail that ethernet switches and all wi-fi is bridging. The means that every packet has to have a source and a destination. If the destination is on the other side of the bridge, the packet goes through. None of the other ports on the ethernet switch or the other side of a wi-fi bridge will see those packets. This is why you generate a huge volume of traffic between two ports, and the other ports are unaffected.
So, let's pretend you have some interesting traffic going between two ports. The ports can be two ports on an ethernet switch, or two ports on a wireless bridge. If you plug a laptop (favored tool of network hackers) into a 3rd port on the switch, or setup a 3rd connection to the Wi-Fi access point, it will only see traffic intended for this 3rd port. None of the traffic (except broadcasts) going between the first two ports will be seen by the 3rd port and the sniffing laptop.
Note: These are the basics. Life gets really complexicated if I introduce a BRouter (bridge-router), VLAN (virtual local area network), wireless switch (dumb wi-fi access point and managed ethernet switch), and VPN (virtual private network).