I remember asking the so-called BT engineer the above question as well and he gave me a vague answer (he did not seem to be sure), not as descriptive as the one you gave.
Same here. The local cable company touts its fibre optic service but my connection is copper. It's still pretty fast, well, fast enough for my needs, but at work it was causing problems. We just switched from AT&T to a full cable ISP and the difference is appreciable. Most of our filings are done electronically now so a fast service is a must. Moreover, all of our files are kept on a cloud server but we still have to keep paper copies. That's not going to change any time soon.