I think he's more likely to be involved in relatively high-level (but still critically important) engineering decisions rather than "science". That distinction aside, I really wonder what makes people so sure he isn't involved, when every indication (interviews, etc.) is that he actually has a pretty good understanding of the principles SpaceX's rockets are built on, and the reasons they're designed the way they are.

Can you enlighten me? Why is this such a common refrain?