I definitely think things have improved (although they can always go south at a moment's notice- for example last year, he dropped and broke his phone, which triggered an "episode" that lasted pretty much the whole day.)

There are likely multiple factors at play- it's quite conceivable that puberty hormones make the matters worse, and that he's slowly exiting this phase, it's something less in the way.

But I also think that as he grows up, there are less "triggers" for his episodes. Episodes are almost always triggered when something or someone contradicts him (for example in the original linked article, when the mom tells the kid he can't wear the pants he wants to wear). Now that he lives by himself in a small village with no parents, no teachers, etc., (when you think about it, schools are terribly oppressive environments) the triggers are much less numerous.

From your perspective, when & how did it start? Was he always like that, or is there a specific event you remember as the start of this?

I've always remembered him being like that, and my parents corroborate this. Apparently when he was a newborn/toddler, he would throw huge tantrums, was very hot-tempered, impossible to manage when he was sick, etc.

This leads me to further believe that his case his mostly genetic/physiological in nature.