How did a DirecTV DECA Ethernet Adapter crash an entire network?

Hi all,

I'm a pro-AV integrator and one of my clients has a 3Com 2024 Baseline Switch. Yes, it's unmanaged and I didn't specify the model. Customer called and apparently some of the network was not functioning. My remote laptop on the switch had no Internet. A Crestron touchpanel was able to communicate with the Crestron processor.

Once I got remote access from guest WiFi, I discovered that the laptop could not ping any devices on the network. So, right off the bat, laptop can't ping any Crestron equipment, but the Crestron equipment continued to work.

When I got on-site, I systematically began troubleshooting. I fired up Wireshark and from my laptop on the switch did see some traffic incoming from the switch.. just some ARP packets and such. Then, I started a continuous ping to a device, and began unplugging network cables from the switch one at a time. When I got to the DirecTV DCAU1R0-01 and unplugged it, all traffic came back immediately.

This DECA bridge puts all DirecTV boxes on your coax network on your Ethernet network with a single cable. I have never seen a problem with them.

After this, I power cycled the DECA bridge, and plugged it back in and it functioned like it is supposed to.

My questions to you all are:

1. Any ideas what exactly happened to this little brick that would cause the switch to stop functioning? It wasn't even like a packet storm or at least I couldn't see it coming in on Wireshark.
2. I've actually seen a similar issue... In my office, when I got my first USB-C ultrabook, I bought a USB-C dock with PD. I plugged network into the dock. The problem was if the USB-C wasn't plugged into my laptop, the NIC in the adapter remained powered up because of the AC adapter, and it locked up my office network! Similar problem?
3. Is there protection in a managed switch that would have prevented this? I'm not new to managed switches but I'm not familiar with protections from this sort of thing. I've seen Cisco switches that don't activate ports when PCs are rebooted and you have to unplug/replug the cable or disable/enable the network connection.. What is this called?
4. Why was the Crestron equipment still able to function? After I left I thought about this and is it possible that the switch worked in groups of ports, like the logical chips or modules that make up the full 24-ports?

I'm trying to learn more about what happened 1) so I can better explain the problem to clients besides "DirecTV adapter got dumb and locked up, crashing the network" and 2) so I can prevent the problem in the future or at least be able to troubleshoot.

Thanks!