It isn’t meaningless - it isn‘t aimed at someone doing a 20 mile leisurely bike ride, it’s aimed at those doing big rides like 50 miles plus, way out of their local area.I agree it is absurd, although it is guidance rather than a rule. To limit cycling to the same distance as walking makes no sense at all. In virtually all cases a person cycling for exercise, rather than to get from A to B, would naturally cycle further than that same person would walk for exercise.
Leaving that aside, to use words like "reasonable" and "significant" is pretty meaningless. You say a walk of a mile is reasonable for you. To me a 10 mile round walk would be both normal and reasonable and I know plenty of people who would consider walks of twice that length to be normal and reasonable. If someone were to stop me 4 miles from home when walking and claim I was a "significant" distance away I would be unimpressed - if I were cycling .......
Of course it would very simple to limit both the time and distance via legislation if they wanted to - not that I think they should.
It actually discriminates more against serious riders than ambling leisure cyclists - how far can anyone walk in racing cleats?!