What do you mean MS is killing off AD? As far as I know they’ve just renamed Azure AD. (But there’s a good possibility I’ve missed something.)

Yes. This is true for coax. Due to how coax is wired, every signal goes to every house, just like tv goes to all the houses on the circuit. It’s up to the coax equipment to filter out the signals that aren’t for that connection (just like a cable box is programmed to only allow the channels you pay for).

But the issue is, if a cable isn’t terminated correctly, it looks exactly like an antenna. This will cause noise on the whole coax system and affect everyone on the same circuit.