I believe that it was a one-time only advertisement for MD. Sure, the screen said, "To Be Continued..." but that might only mean "To be continued in your own game..." So they expect you to pick up the game to imagine the rest of the story.
The Ekans/Arbok mistake was rather irksome. I felt that PUSA would have tried harder to avoid a 4Kids mistake.
So how did you like this special? I was shocked that there was going to be a show about Pokemon Mystery dungeon, but when It came out I was quite impressed, It was cool to finally hear a Pikachu talk! ^^