Why couldn't those scientists who tested this material, give the amount of red/grey chips for each sample? They said one sample yielded 0.1% red/grey chips by weight in the sorted sample. Then they don't mention the percentage for the other three samples. This shouldn't be a difficult task to complete, and it frankly doesn't support the first sentence in their conclusion:
We have discovered distinctive red/gray chips in significant
numbers in dust associated with the World Trade Center
destruction.
They mention at the beginning of the article that they received several samples, but they only selected four for analysis. There is no indication why they chose those four samples, there is no mention of random selection (a very big no-no), and they didn't quantify the percent composition of the samples. This would be fairly important. Does the composition of the dust change as the distance from the tower increases, or does it remain constant? They can't answer that question.
Despite the fact they found a 2.5 mm chunk, they maintain that the material is nano-material. That doesn't follow.
They measure 4 different energy yields by mass for the chips they found, in one case one chip yielding 4 times as much energy as another. Again, this amount of variation doesn't lend itself to the explanations of a lab produced material.
I'm sure there's more to pick apart, but that's a good start.