Earlier quoted context omitted.
They are $2 short but own one bitcoin that might be worth $50,000 to someone else. If I buy a car for $20,000 I'm $20,000 short but I also own a car.
And when that person does buy it for $50000, we are in the exact same situation, but now the missing money is $50000 rather than $2.
Everything, even stocks that are being traded at a high frequency, has moments when it is not being traded.
If continuous markets were somehow realized, then moments when value is "missing" per your definition could be rare.
But instead, there are infinite non-trading moments between each pair of trades, so "nearly all" of the time your definition says an asset is worthless. That just seems like a useless, inappropriate definition from a practical perspective.