I'll try to answer this with a bit of a silly example.
Water would do quite poorly in a NOACK test since it would all evaporate away quickly at 250C, but it would look fantastic by flashpoint since it doesn't really burn (my understanding is that the molecules would dissociate at extremely high temperatures).
I think any motor oil that gets in the combustion chamber is going to burn given the 600-700C temperatures in there, and you're probably in real trouble in any oil actually involved in lubrication catches fire. I believe there is some correlation between high flashpoint and low NOACK loss, but I think the latter correlates more closely to things that can actually happen in an engine (especially one with a turbo as an extra super hot spot) than flashpoint.
Also be careful to see if the D92 or D93 test method is used to determine flashpoint, that latter tends to give a lower result than the former for a given oil.