Tiny White Insects Under Peeling Stucco
Do an Image search for "Psocids" or "book lice" or "bark lice" and see if they fit what you saw. They are not really lice, they are a type of mite and they feed on molds that grow in damp places like under the bark of trees (or old wet books), which your flaky stucco may have been similar to from their perspective. They kind of look like tiny tiny termites, but without the mandibles. They are harmless.