The only stuff that is very bizarre on this entire leak,is the "all unlocked" blasphemy,and the way the leaker describe the characters is very bad.
The rest is very accurate indeed,and about the stage announced today,he could said what game the stage represented,similar thing can happen with endless ocean and rhythm heaven stages.
The other stages are very clear like great fox for example,even having no official name,we know that exists on the game because it was already announced.
17 new stages have not been announced yet:
Bowser Castle
Jungle hijinx
Bramble blast
Forest Haven
Yoshi Story
Tourian
Nimbassa City
cookie country
Mt. Dedede
Patch Land
Underworld
Rhythm Heaven
Endless Ocean
Nintendo Land
Nes Remix
Greenhouse(The way he knows what series this stage represents gives more credibility to the leaker)
Gyromite
Shooting Gallery
2 stages are from 3ds not announced yet for wiiu:Magicant and Mute City
From familiar stages not much can be said because the only announced yet are:Castle Siege and Halberd
The 3ds familiar ones that we know are:Distant Planet,Flat Zone 2 and WarioWare