I received treatmentsd from a chiropractor.
He used his "tool" on the bottoms of my feet.
Is it possible for this "thumping" to cause a neuroma?
I very much doubt. Activator in the first place is very gentle (too gentle in my opinion, except for children and the elderly, but that's my opinion), and secondly even vigorous chiropractic treatment of the feet wouldn't cause a neuroma.
I presume you went to him for treatment of your feet. If there's a neuroma, it was almost certainly already there.
But not to worry. Even Morton's neuroma responds well to chiropractic treatment. It may not "cure" it by which I mean the pain and tingling goes away altogether, and doesn't return, but then it usually returns after surgery too.
Stay with your chiropractor.