Look at this Update people.
Notice how Snake can talk to his teammates to learn about all the other Characters..?
Now, someone has to voice Snake and ask his partners questions.
A.K.A. David Hayter.
That means David Hayter knows every single Character in Brawl. And she asked him which Character in Brawl he would most like to beat up.
He said Pikachu, Jigglypuff and Mario.
Judging by the way he said it, he clearly is not as into Brawl as we are, and was only working to get paid. So he most likely never knew that Jigglypuff was a secret.
He was probably just thinking back to which Characters he remembered most. Most likely because their Codec was fun to do.