That's close to accurate but note that some have both a truth claim and an operational claim. See e.g. http://predictionbook.com/predictions/2838 which predicts that P != NP and predicts that it will be proven by a certain time.
In general your point about operational predictions is a good one, since predictions should be actually falsifiable.
I was actually thinking of your predictions when I said 'implicit'. How would that prediction be judged? Obviously by whether the community of mathematicians/complexity theorists like Scott Aaronson or the Clay Institute says that it was proven or not proven.
I like to make predictions about things like quantum mechanics and decision theory and cosmology and fun stuff like that. Can PredictionBook be used for this? If so, what should the guidelines be? Figured I'd make this a Discussion post so as to encourage the habit of betting on logical uncertainty.