They probably already had some inside but not for general use, but to exchange data between the two ends of the cable. Modern power grid is smart, and it has da

They probably already had some inside but not for general use, but to exchange data between the two ends of the cable. Modern power grid is smart, and it has data connection along side power, they do that also on overhead power lines (the upper cable beside the three phases serves as a protectoin from lightning strikes but also has a fiber inside). In practice the power network also has a completely isolated LAN (for obvious security reasons) to manage the whole infrastructure. At least in my country it's done like that.