If you hear someone say 10,000 Feet, you know they must be talking about altitude (generally speaking). If you hear 100m, its likely to be RVR etc etc.
You could also hear 300ft in the US. Now is that cloud base, or RVR?
Wasn't that his point?
use knots for speed, miles (nautical miles preferably) for distance, feet for altitude, meters for RVR, feet per minute for climb/descent.
Then, you know what's being talked about based on the unit of measure.
Of course, if you grew up in the US, it's hard to judge distance by meters, because they're aren't exactly yards... and if you grew up elsewhere it's hard to judge height by feet, because you have to divide by 3 (approximately).