He didn't oversell it (which is what every tech speaker does nowadays as they try, and fail, to imitate Jobs). His ton was even, he didn't sound or look nervous. He had minor trip ups a couple time and just kept going. He made the audience genuinely laugh.
Also, what makes you say he took "his cadences/writing style from popular tech presenters?" Isn't that a bit like watching a child score three pointers one after another and saying "ah, isn't that cute, he's imitating Ray Allen"
He absolutely shows signs of nervousness – his movements are twitchy, he speaks too quickly and runs over his sentences. Clearly he spent a lot of time rehearsing what he had to say, and he does a good job of it. He gets the audience to laugh, though I'll be skeptical and suggest that audiences are predisposed to laugh at jokes made by young people, and also at jokes involving Justin Bieber getting whacked.
The reason I wouldn't call him great (though he is clearly good at this) is that he doesn't take his audience's perspective into account. I'd be stunned if he could; it's a damned difficult skill to have learned when you're a preteen. He takes (and sells) some effective cadences, but what he's actually saying fits awkwardly within the frame. He spends time explaining certain things unnecessarily, because from his younger perspective certain details are more interesting than they are when you're even a little bit older. Again, not surprising, and not a ding against him.
As for your Ray Allen quip, unfortunately I don't know basketball well enough to respond, but I argue that there's a difference between a basic action (like shooting a three-pointer) and a pattern (like constructing a speech in a certain way with certain rhythms). It would be like if a basketball player had a certain famous technique for making his way across the court once he had the ball. You could watch a younger player and notice that he was mimicking the tactics of certain players. Once again, not something to be held against a young person figuring out the rules of a game – that's one of the best ways to learn! But this kid is still sticking pretty rigorously to a template. It's a good template, and I think it's cute seeing a young kid mimic speakers with whom I'm quite familiar.
I just wouldn't call it great – because for me presentation is a nuanced art, and there's a lot more to it than what we're seeing here. Calling this great might close minds to the possibility of more sophisticated presentations, and that would be a real shame. It's nothing against this kid, who's clearly bright and having a lot of fun in the spotlight.
I really didn't want to come across as pedantic, which is why I tried to keep it light and say I thought his mimicry was cute. And I love stuff like this! We need more 6th graders like this. I would have mad chilled with him and his app club.
That said, I do believe that the way we use language frames the world for other people. So I try to keep things in perspective. It's not that this isn't wonderful, it's that there're so many wonderful things that I prefer specificity of compliment to a general word ("great") that may suggest this is some sort of pinnacle to others. Greatness in turn becomes the people with such a tremendous sensibility that they can incorporate many, many wonderful things and, in the process, underline some deeper truth.
We're talking about both (1) his presentation and (2) his programming skills. Other kids should be encouraged by his presentation, instead of thinking, "Cool, but unfortunately he's a genius (or super-special, or etc.); I could never do that myself."