I guess there's something about calling a series "cancelled" that makes it sound like it would have never ended otherwise. I still think Beelzebub was on its way out, and the ending got expedited by the cancellation round.
I don't know why but sometime last year I was thinking "yep, this is the final arc. It'll probably end with Fuji." So to me, as much as its pretty obvious Beelzebub got cancelled, I also think the author was planning on exiting anyway. I mean, I even wanted to resist calling it cancelled because it just made so much sense he would end with Fuji, consistency and continuity be damned. But being cancelled is probably more accurate to call it.
But yeah, a popular long running series is going to get colorpages for its final chapter. I don't know why the spoiler dude didn't label it as the last chapter, but it totally is. I don't know what Mago's exception was, but the extra chapters in Jump NEXT was probably to fill up the volume.
Edit: I agree with Kaiten completely. I also think a lot of Beelzebub's fandom from this part of the woods (non Japanese, Edited Manga readers) really don't get it was a popular series and it did well for what it was. If Beelzebub wasn't considered a success it would have been cancelled a long, long time ago.