In this case, the question is:
> If a number generator is uniformly distributed, why might that not be 'random enough'?
If we rephrase this as:
> If a number generator is uniformly distributed, why might that be 'too predictable'?
This makes the flaw obvious: there are many ways to choose numbers uniformly which are completely predictable. For example, choose the smallest value first, then choose a value which is furthest from any previously-chosen value (in, say, lexicographic gray-code order).
The point here is that 'uniformity' is not the property we care about; it is a consequence of the property we care about (unpredictability). If a distribution were non-uniform, we would be better able to predict it (by biasing out predictions to match the distribution), hence the least-predictable distribution is necessarily a uniform one.
Other times this comes up:
> Are quantum measurements 'truly random'?
That's untestable, but we can test whether they're predictable or not.
> This encryption algorithm requires a source of random bits.
It would work just as well with a source of bits that are merely unpredictable.
> This strategy can only be defeated by a random opponent.
It can also be defeated by an opponent which you can't predict.
And so on.