The conservative side of Dramatic Flourish lists the same effect for both one and two boons.

There is a small possibility that this is intentional, so that if you roll 3 boons you can invoke both and cause the target 2 stress...

That's probably the case - Boons are 'fuel'. Unlike successes, you 'spend' them, but you can only 'buy' something once - so yeah, probably intentional.

It is intentional. Since each individual boon effect can only be triggered once, providing the effect on two separate lines allows both effects to potentially be triggered, assuming enough boons are rolled and that is the result the player wishes to spend them on.

Cool, thanks. It just looked odd as it is the only card I've found so far that has multiple triggers for identical stacking results.