From your description it sounds like BW stuck down on underlay (as it should be) stuck down to concrete floor (as it should be) .
You can be tricked into thinking BW is a wool mix of course that's the whole point and why it was originally called a Fake or False Wilton.
You say it is 'Hessian' backed are you sure ? When you pulled it back could you see the pattern through the back ? If so it has no backing as such but is woven into the jute, this is what causes the shrinkage when even slightly damp.
If the old fella is a retired CC he would(or should) have know full well that he had a cheap but of tat down that should not be wet cleaned,. To late now I am afraid use it as a lesson learned .