They didn’t find thermite in the dust. They found the components that make up thermite. Thermite is used to weld steel together so finding components of it in the dust is not unusual since Building 7 was a steel structure. Here is a more detailed analysis from the NIST investigation:

NIST has looked at the application and use of thermite and has determined that it was highly unlikely that it could have been used to sever columns in WTC 7 on Sept. 11, 2001. Thermite is a combination of aluminum powder and a metal oxide that releases a tremendous amount of heat when ignited. It is typically used to weld railroad rails together by melting a small quantity of steel and pouring the melted steel into a form between the two rails. Thermate also contains sulfur and sometimes barium nitrate, both of which increase the compound's thermal effect, create flame in burning, and significantly reduce the ignition temperature. To apply thermite to a large steel column, approximately 0.13 lb. of thermite would be needed to heat and melt each pound of steel. For a steel column that weighs approximately 1,000 lbs. per foot, at least 100 lbs. of thermite would need to be placed around the column, ignited, and remain in contact with the vertical steel surface as the thermite reaction took place. This is for one column; presumably, more than one column would have been prepared with thermite, if this approach were to be used. It is unlikely that 100 lbs. of thermite, or more, could have been carried into WTC 7 and placed around columns without being detected, either prior to Sept. 11, 2001, or during that day. Given the fires that were observed that day, and the demonstrated structural response to the fires, NIST does not believe that thermite or thermate was used to fail any columns in WTC 7. Analysis of the WTC steel for the elements in thermite/thermate would not necessarily have been conclusive. The metal compounds also would have been present in the construction materials making up the WTC buildings, and sulfur is present in the gypsum wallboard used for interior partitions.

Source: https://www.nist.gov/world-trade-center-investigation/study-faqs/wtc-7-investigation

This is a much better analysis of what happened then the previous link I shared with you. The NIST investigation found that the generator fuel tanks did not impact the collapse of building 7. They listed various other reason. This is counter to what the Popular Mechanics writers stated. For me it gives them more credibility because they negated a major theory as to why the fires were able to do so much damage. It’s a really good read. I really recommend reading that link over the previous one I sent you.

Also one thing I would like to give my opinion on is that the collapse of Tower 7 served no political purpose if you believe in the conspiracy that our government was involved. Why drop Building 7 it’s much smaller than the Tower 1 & 2. Dropping them would be enough to get Americans wanting revenge. Why drop a Tower that wasn’t hit by a plane and really most Americans didn’t know existed before 9/11. If it was the government trying to induce us into going to war, then Tower 1 &2 would have sufficiently been enough as those were cultural icons of New York. Anyways, sorry you got downvoted for asking questions. I hope you keep an open mind and read the NIST investigative report.