There is no hard evidence, but there is evidence that it could be.
1)We know the sword is magical because
..a) we know wanda dropped two magical items from here
..b) that the two items are recovered by the coalition here
..c) and that Webinar and Dora get the sword and hat here
2) (at least some) magical items can be resized from here
points 1 and 2 taken together indicate that it is within the realm of possibility that the sword could be re-sized.
Given that, I would say that idea that the dagger is the sword resized came from third base, not left field, to stretch the metaphor.