The beta footage in that link is official - that's a video captured by Nintendo from back when they were working on an early version of the game. The ROM isn't out there (not yet anyway?) because the game was simply never released in that stage of development. Releasing it like that isn't something Nintendo would do anyway.
Of course Yoshi Master's hack is different,
Yoshi Master doesn't work for Nintendo or anything
. His "Super Mario World Beta" hack is simply his interpretation of what the beta ROM could possibly have been like, but it wasn't made to be completely identical to the footage in the video.
If you want the
ROM from the video
to come about, your best bet is to just wait and see if something comes out eventually (kind of like it did last year with the NES version of SimCity). Either that or you could just break into Nintendo's headquarters and steal the files off of their computer. Then you would be a hero to us all
E: Nevermind, I'm an idiot (see below). I'm confusing the video you linked with some old screenshots that surfaced on the internet a long time ago. I looked into it a bit more and yeah, that video's a fake - Yoshi Master based his hack off of only the few screenshots/concepts that were revealed, but the video version of it was just someone recording the hack and trying to pass it off as official by blurring the quality to make it seem old. Oh well.
Now that I understand what you're actually saying, the reason why the levels are changed could be any number of reasons. Maybe whoever recorded the video thought that they could do a better job of designing levels that looked like they could have come from a beta version of the game. Or, even more likely, maybe the levels recorded in the video are just from an older version of Yoshi Master's hack. YM seems to still be active around here, why don't you PM him about it and see if he knows anything?
Science teachers are too afraid to teach their students about the element of surprise.