You could easily have said this with words instead of a video.
Your logic is completely flawed. You're basing thise solely off appearance and species name. Slowking has the word "king" in it, yet comes in both male and female variants. Gardevoir wears a dress, but again, can be either male or female, especially before the fourth generation when players didn't have any other choices.
Once genders were introduced, Goldeen and Seeking could be either male or female. If "a female Pokémon turns male" as you claim, then Gamefreak would have made a clear distinction and not allowed Godeen to be male or Seeking to be female, as they did for Nidoqueen or Tauros male.
You can find examples of this in nature too, I'm sure. Either way, your logic is flawed.
~Psychic