If the creator says the events of BoG take place between Buu and the Budokai within his manga, it's part of the manga. Your argument is invalid. Honestly, it's plain stubborn to say it's non canon after all that's been said about it:
Toei Animation’s Press Release for the upcoming film - July 17, 2012:
“The global phenomenon Dragon Ball is being made into a movie using Toei Animation’s latest technology, consistently realized as a Toriyama work, with the original author Akira Toriyama himself deeply involved from the script stage for the first time."
Toriyama interview:
I tried thinking up an original story, imagining it as though [the manga’s] serialization had continued. What’s more, the God of Destruction Birus, who I drew the design for myself (something I don’t usually do), is a terrifying opponent so overwhelmingly strong that he surpasses the dimension of the previous enemies. But it’s my trademark to not let things get too dark. At the very least, I’m satisfied that it’s been finished up as a very entertaining piece of work.
Toriyama interview:
What are your thoughts on having participated in the movie?
It was fun~! This time, I devoted myself exclusively to creating the story, so I was happy most of all at how it became several times more enjoyable by other people’s hands. In particular, the climactic battle exceeded my expectations by far!!
Toriyama interview:
It’s rare, or rather, it’s the first time, that I’ve been deeply involved with the animation from the scriptwriting stage.
As it had been a while, there was a lot I’d forgotten, but as expected of the creator of the original work, I was soon able to remember the tempo of things, at least.
For this film, while leaving the atmosphere of the original intact, we’ve added just a little bit of modern flavor, so I think it will be an enjoyable piece of entertainment, just like old times!
Toriyama interview:
Q: Why is Kaiō’s planet so small?
A: The fact is, it was destroyed by the God of Destruction!!
It used to be so big that its diameter was about 100 times that of Kai’s current planet. Apart from the size it was completely the same as it is now, with nothing but grassy fields and roads. Kai-sama enjoyed his hobby, driving, but then one day Birusu, the God of Destruction, stopped by and they played a video game together (it was a car racing one). Birusu lost, and so the planet was destroyed by the peeved God of Destruction. Kai then took a large leftover fragment, whittled it down to a sphere, and built a road on it so that he could have fun driving there. This became Kai’s current planet.
I heard that this is the first time you’ve been deeply involved with the script of a movie; please tell us the reason.
The catalyst was that, first of all, when the script originally came to me, there was a lot of the sort of dialogue that only the creator would know, so I thought, “that bothers me”, and then this and that also started to get on my mind, and so rather than telling them to revise each individual thing, I thought it might be faster if I just wrote the script myself.