Why does that sound like bs

Because it puts the onus on you to string together a lot of "maybe" and "if" to get something as a workable explanation. IF by "copper wire" they didn't mean ethernet cable, but instead it was some analog cable, then MAYBE the wire getting cut started getting interpreted as garbage that was going out to a larger network.

There are already a lot of "this is what happened" stories floating around, and they can't all be true. It is plausible that one thing going wrong at one busy airport would have cascading effects. It happens with weather all the time, and some of those delays last longer than the four hours and change the flights were grounded.

The article says "a contractor for the Federal Aviation Administration was working at a remote location" which doesn't answer any questions, but opens up a whole lot of other questions. Can a malicious actor just saunter up to the right "remote location" with a pair of wire cutters and ground the whole US? And all of this was on top of SpaceX having debris cause flight issues, AND it was the first day of a test of an AI flight routing program.

The aging ATC system needing to be overhauled is a trope at this point. I can't ever remember a single comment/anecdote/experience that tilted towards "this is fine and it should stay this way forever," except for maybe the people with the power of the purse who aren't accountable for aging infrastructure apparently.