Here's an interesting quirk of the copyright that makes me think this is a minor mistake and not a legitimate leak.
On the Challenger's Pack #4 description, it says ©SNK Corporation
All Rights Reserved. Now, this may seem like standard legal jargon, but the All Rights Reserved is actually noteworthy. Basically, stating "All Rights Reserved" is actually rather unnecessary. It's a leftover from a time where you had to actively proclaim your copyright or risk losing it. Nowadays, basically every country has shifted to granting this ownership of copyright as a default to artists and media companies, making "all rights reserved" largely redundant. A handful companies still use out of tradition, but it's a very optional thing.
So... what's this all have to do with Smash Bros? Well, Smash Bros doesn't use "all rights reserved" anywhere within its copyright. This alone doesn't mean much, as Nintendo could've included it as that's the way that SNK expresses their ownership. However, things get complicated when Hero is factored in. Hero's copyright information solely lists companies who have ownership of the Dragon Quest series (Square-Enix, Bird Studio, etc.) with no mention of Nintendo, HAL, etc.
However, this claim of Hero's copyright is actually different than the way Dragon Quest's copyright is usually expressed, as that usually includes an All Rights Reserved.
For whatever reason,
Smash Bros tends to forego "All Rights Reserved" in its copyrights, even when discussing franchises which traditionally utilize this language. This really hints this copyright was done by a legal team separate from the one involved in Smash Bros, thusly meaning that the SNK copyright of Challenger pack #4 was more likely misattributed than properly leaked.
TL;DR: The copyright for Challenger Pack #4 is mismatched with the rest of Smash's copyright formatting wise, so its probably not real.