Unless you were taking down walls and/or ceilings..you did not see black mold.
I have seen black mold. It was between layers of wall board in a bathroom. For many years the previous owners just put up another layer of wall rather than do a real job of renovating (that bathroom was 6" wider when I torn out all the wall board that was just put up one on top of the previous).
I know that mold can look black... but..it is really a very very dark green.