Dumont did it first in the sense that he achieved a flight long enough, i.e. over 100 meter, in order to win the prize for such a flight that had been instituted a couple of years earlier.
A half of year before Santos Dumont, also in Paris, there had been other flight attempts that had succeeded to take off completely unaided, by rolling on wheels (by Traian Vuia), but the achieved lengths of sustained flight had been much shorter, too short to qualify for any prize.
So while the achievements of Santos Dumont are very commendable, the word "invention" is not really appropriate for them, because all he had done was to do better some of the things already done by others in their attempts to win the French flight prizes.
The Wright brothers have started from Otto Lilienthal's work. While their improvements have been extremely important, their work has also not started from zero, but it had built upon the work of the predecessors.
In the history of inventions, it is typically impossible to say that something has really begun with some inventor. Instead of that, the right way is to point to each inventor and show what they have done better than what existed before them.
A half of year before Santos Dumont, also in Paris, there had been other flight attempts that had succeeded to take off completely unaided, by rolling on wheels (by Traian Vuia), but the achieved lengths of sustained flight had been much shorter, too short to qualify for any prize.
So while the achievements of Santos Dumont are very commendable, the word "invention" is not really appropriate for them, because all he had done was to do better some of the things already done by others in their attempts to win the French flight prizes.
The Wright brothers have started from Otto Lilienthal's work. While their improvements have been extremely important, their work has also not started from zero, but it had built upon the work of the predecessors.
In the history of inventions, it is typically impossible to say that something has really begun with some inventor. Instead of that, the right way is to point to each inventor and show what they have done better than what existed before them.