The idea here is that the cable used to charge has been compromised. It now has the ability to pull info from your phone and stream it via Bluetooth to a malicious actor. Bluetooth is not wired, but that is the exfiltration vector. Even if you plug into a wall outlet, the electricity powers both the BlueTooth transmitter, and the circuit that is pulling data from your device.
The USB condom wouldn't stop that because it would be transmitting before getting to the condom.
Yes, ^^^This^^^ It's not a normal cable, but one that has been specifically designed as a hacking device, yet look like a normal harmless cable.