Sounds like someone doesn't understand statistics or didn't actually follow the leak in question.
The part of the ESRB leak that people are "100% sure" about is the video leak, because of the amount of detail and the time that would be required to fake that part. We didn't get actual game footage of anyone other than Ganondorf, Shulk, and Bowser Jr, though, and there are other parts of the ESRB leak that were flat-out made up as an elaborate joke (The DLC bit, in particular). The menus in the screenshots DO match up with what we've seen in the PotD which lends a LOT of credence, but it doesn't "100% confirm" anything. Furthermore, we don't know how old the build in question for the ESRB leak was and whether all the characters on the screen were finished or in a bug-testing state. It's VERY unlikely, but it's possible the DHD could still be potentially cut between when the build for that footage was filmed (which could've been upwards of a month or two before we got the leak) and the final release because of a major bug they couldn't fix. Once again, not very likely at all, but it's something that COULD happen.
You'd be crazy to not think it's true at this point, but it's the difference between a "reasonable doubt" and a "shadow of a doubt" in this case. Hence, the 5% reduction there. Some people write this as 99.9% as well, but that's usually saved for things of even more certainty than this, though ("A flipped coin will land on heads or tails" is 99.9% because it COULD and, on very rare occasions, has landed on its edge).
A 100% confirmation is an official announcement by Nintendo or official footage of the character.
Once again, I don't really doubt that DHD is in, but that's not the same thing as a 100% confirmation. If we're being completely precise about what we know for certain about the character, it's that there's a beyond reasonable doubt chance (95%) that he's in and that the portrait in the leak is his select screen model. My point was that a person should be excited for footage of a character that we know almost nothing about other than a name and a not quite 100% confirmation.
Also, all of this said and done, I suspect, if they show off new characters, they'll mostly show off the other returning veterans. Not everyone follows the website or Japanese coverage, but DOES follow official releases like Nintendo's youtube and twitch channel. So, they may want to keep the remaining secret newcomers a secret to the remaining 5% of consumers that don't want those things spoiled.