It is a fact that Naruto is extremely busy. It is your theory however that Naruto never trained or taught Boruto his signature jutsu.
You have to twist theories to suit facts. Not twist facts (Naruto's absence) to suit theories (Naruto never trains Boruto).
I'm not following. It is a fact that:
I. Naruto never taught Boruto anything.
There is no proof to establish this, only assumptions.
In the canon, Boruto has two teachers:
I. Konohamaru taught him the Rasengan
II. Sasuke taught him how to improve his Shuriken throwing
Everything else has been self taught until proven otherwise. I'm only portraying that since Naruto is extremely busy, he never had time to train his son. Which goes along with the story, since Boruto is a Prodigy, he didn't really need a teacher. But because he lacked motivation, he didn't hone his own skills.
With Naruto's sage mode, he could find Boruto instantly. Even Shikamaru relays that to Boruto. It's a game, and probably the only time Naruto gets to spend with his son. It's not like Naruto said no. It's Shikamaru who told Boruto stop pestering his father.
Well I didn't really think a clone version of Naruto would want to end the game quickly with his son lol.
Dye Boruto's cloths orange.
Keep painting, pranking and mischief making.
Keep the same signature techniques rasengan and kage bushin.
Boruto's wears Naruto's jacket towards the end of the movie, they still establish he isn't Naruto at all though.
They also establish that Boruto isn't a prankster by nature, nor a person who likes mischief. In fact that's a keen difference between them both. Unlike Naruto, Boruto only throws that side of him towards his father, because he wants him to look in his direction.
Shadow clones and Rasengan are all they share, but even then they use it differently:
Boruto doesn't spam Shadow clones, in fact he uses them in strategic ways in the exams
Boruto doesn't spam the Rasengan in his fights, nor does his wind release Rasengan operate like FRS
Factor that in with his Gentle Fist Taijutsu, two other elemental natures, and shuriken jutsu. Calling him a Naruto clone is a joke.
And Boruto looks a like a clone of Naruto.
And Sarada looks like Sasuke. Your point?
Gaiden is during the Academy days. You know, when Naruto and Boruto play hide and seek. Kage Bushin is a forbidden technique, so it's not something they teach in the Academy. Naruto is likely the one who taught Boruto. Since the normal bushin is probably still a requirement for graduation.
An assumption. While Kage Bushin is a forbidden technique, there were many instances were other kids also performed the technique. I doubt it's that secretive. The hand signs for the technique is a literal plus sign ... Do you think Boruto is some kind of idiot who can't even figure out how to make that hand sign and practice making a copy of himself?
Funny enough the novel version of the movie says nothing of Boruto learning the Kage Bunshin technique from anyone, in fact they even go out to say Boruto tried to learn the Rasengan by watching someone else do it, he failed of course since he was trying to recreate the technique from sight rather than learning the essential steps. It just goes to show you that this boy got to where he did by his own talent, rather than hard work. Make no mistake, while he did try to learn the Rasengan by himself, he quit after a few tries instantly (novel).
Not by training or asking someone to help him. You can't really prove Naruto taught him anything. Someone can easily go against and say that he self taught himself, there is no real distinctive answer.
Other than the fact that the labeled him as a Genius who can do anything when he sets his mind to it, plus, they state throughout the movie that he is lazy, unmotivated, and doesn't train at all.