Suppose rpietila's formula was amended to yield zero in the case that the prediction is within the range. Then your offered counterexample fails. Did you have others that would prove the amended scoring formula invalid?
Note, to anyone interested, that the reduction of the price to log10 form allows the predictions to be compared on widely differing timescales, in which price values might be 10x larger or smaller. rpietila has been talking about deviation from the log10 trendline in terms of these log10 deltas.
Fair enough, let's do another one:
Imagine the actual outcome is 95. A prediction of 50-100 would score 5. A prediction of 89-100 would also score 5, although it is obviously much better than the first one. So the amended formula does not correctly rank the predictions either (at least not intuitively).
Let me see if I can think of another one...
Log scale or not doesn't really matter for comparing predictions to each other (by which I mean ranking/ordering them).
Edit: Came to think of another counterexample for the amended formula: if the prediction is 50-100 and the outcome is 101, the amended formula gives score 0. If the outcome is 150, the amended formula also gives score 0, although the first case is obviously better than the second. (You might argue that this is "fair", though, but that is a subjective argument: the amended formula still clearly fails to correctly rank/order the two predictions).