I don't think anyone can be stupid enough to put the tail on the top by mistake or by ignorance. It's just beyond imagination. So it must be on purpose.

The modeling team most likely put the tail on the bottom at first but Yoshida said no because he didn't want people to glamour just the tail. So he instructed the team to move the tail to the top. There's no other explanation.

You can't be competent enough to make a great game like this but all of the sudden go ultra derp and put the tail on the top by mistake. That's like creating a whole new franchise that swept the world then suddenly fire the director that made it all possible!