Sounds very much like a scam to me and so lazy that they didn’t even bother to work out that Virgin Media and BT have nothing to do with each other. He could have tried to sound more convincing by saying he was calling from Openreach, although they don’t often call end customers.
It’s common for scams tell you they have found something wrong and then try to gain trust by telling you they are calling from a big, well known company. They proceed to give you their employee badge number or some other complicated and random alphanumeric string that you have no way of verifying.
Smacks of typical modern day scam to me.
