The truth of the matter, as far as I can tell, is (F) Not exactly none of the above, and not exactly all. The following is my opinion and deduction and should not be taken as proven fact.
Steven Jones appears to have started from the unquestioned belief that the collapse of the Twin Towers was caused by destructive devices placed within it by conspirators within the US Government. This belief, I suspect, was idealogical rather than evidence-based. However, he quickly ran into the difficulty that the only known devices for causing such a collapse were demolition explosives, and he was sufficiently non-delusional to realise that the sharp and extremely loud sounds made by such explosives immediately prior to collapse were absent from audio recordings of the collapses, and that this was concincing evidence that such explosives had not been used. Therefore, in order to save his hypothesis, he had to postulate a device or substance capable of severing the steel support structure of the towers without creating loud noises.
His answer to this conundrum was to hypothesise the use of a thermite reaction, which is known to generate sufficiently high temperatures to melt steel. This required him to attribute nonexistent and often self-contradictory properties to thermite, but he has so far managed to delude himself sufficiently to ignore this problem. His mission, therefore, has been to find evidence that there was thermite present in the Twin Towers. His belief is that this will prove that their collapse was due to thermite-based devices. Again, there is a problem with this backward reasoning, because logic is not reversible; "all A are B" does not imply "all B are A", and as a result Jones's logic is generally based on the fallacy of affirming the consequent, a classic symptom of trying to formulate a proof based on backward reasoning.
Jones's approach, therefore, has been to sift through the evidence, modifying it occasionally to suit his purposes, for items that appear superficially consistent with the presence of thermite in the Twin Towers. These specific items are presented as irrefutable proof, while any and all items of evidence that contradict the hypothesis are simply ignored; these include the internal contradictions of the hypothesis itself.
The origin of thermite particles, therefore, is not physical but psychological; they originate from the imagination of Steven Jones, and the evidence for their existence is carefully selected, and where necessary edited, by him.
Dave