It's not really a bold prediction.I think my Smash prediction is like the most discussed prediction I made since I told everyone to keep their Switch expectations for last November in check and PS4 was "nuking from orbit"
When Smash Ultimate results come in its going to be either really fun or time to hide in a Fallout shelter until the dust settles
Smash Ultimate (for the kind of game it is and the platform health it is going to be released for) has a good chance to be the fastest selling Nintendo games for a Nintendo home console (or at least among the fastest selling ones).
Now if you had predicted that Smash Ultimate would overall sell 30M (worldwide) or be the best selling Switch game by the end of the platform cycle then that would be a bold prediction.