I have been thinking "Eh?" for different reasons.
Firstly a "technical" customer would or should have been aware of whether or not FTTC cabinets had appeared in the locality; if they hadn't then it would be unlikely that FTTC was available. They are hardly difficult to spot, after all.
Secondly if it was known that the existing service gave something around 18 Mb/s on ADSL then the area in question would be unlikely to be a target area for BT to put in FTTC in the first place; with 10 Mb/s being a sort of standard for a USO why would it?
I do not seek to exonerate BT's mis-selling in any way, but I get the feeling that the customer in this case was not as savvy as he perhaps ought to have been.