I think that's actually a much better port than anyone could have ever expected from the 2600. How long did it take them to get it to look that good? The 2600 certainly doesn't lend itself to that.
"Ever wonder what Maga Man would look like on the Atari 2600? Well the guys at the I Am 8-Bit art show did and had a custom Mega Man 2600 game made for their art show on April 17 - May 12, 2007 that could be played on a giant controller. Here is a link to their web page"
What about that says it wasn't running on an actual 2600? There are a lot of people with way too much time on their hands who love doing homebrew programming for ancient systems like this.