People don't believe this because it's false, those 3 hours are just the last session connecting all the dots. They've tried a lot more, probably thousands of hours, in total.
Honestly? I don't think so. If anything I think they would obscure this using averages (e.g., maybe they solved some hundred problems and the easy ones took a few minutes and the hard ones took a couple of days), but if they have a model that's as good at math as they are as coding I don't see why it'd be impossible.
I think novel mathematics is intrinsically harder than coding (much in the way that computer science research is harder than coding), but the models are scary good at coding.
