https://en.wikipedia.org/wiki/My_Little_Pony:_Friendship_Is_... explains in detail - between 2010 and ~2015 there was a massive overlap between millennial geek culture and unironic fandom of the rebooted My Little Pony show, especially among millennial men. One dedicated fan hub averaged almost 400k page views per day over its first 3.5 years of existence. And throughout it all, programming projects abounded, such as the delightful FiM++ esoteric language (https://esolangs.org/wiki/FiM%2B%2B) styled after the show's framing device. For many in tech now, it was an inescapable part of internet culture of the early 2010s, and a fond memory for many.
I mean, 15.ai started as a 4chan project for /mlp/ users to generate voice lines from official voice actors now that Friendship is Magic is over (google Pony Preservation Project). Honestly, the more impressive part is that a bunch of nobodies on an imageboard leapfrogged the rest of the industry and made a now-famous voice transformer model.
In the greater sense, though? Ponies have always been this weird relic of internet absurdity and bear-baiting. Some people rep it ironically, other people are dead-serious, but the community has significant overlap with the STEM field. As a result, a lot of pony-related stuff would end up propagating into the tech world, much like this very project.
Aside from the causal brony references, this project originally featured a lot of my little pony voices because it needed meticulously annotated transcriptions of the input audio to be trained well.
The extremely dedicated brony subculture voluntarily put in a lot of work to get a corpus for the AI to learn from.
There's also another factor at play: this AI works best with highly pitched voices, which my little pony is just full of. Not only did MLP provide such a generous source of training data, its results were also much more impressive than the dry dictation many other corpi would've resulted in, adding to its fame.
I personally haven't seen any significant rise in MLP references, though that could be because I don't know the show so I don't catch references to it. It's also very possible that you've caught the Baader-Meinhof phenomenon.
My ML professor at the university I went to was also weirdly obsessed with MLP.
Weeaboo/furry data scientists are always ahead of the industry - I seem to recall an effective decensoring model that was called "DeepCreamPy" and had almost 10K github stars before it was nuked and rehosted.
I'm convinced that learning Statistics is in a zero-sum game with social skills.
It's basically the same as unironic appreciation of various child-targeted-but-adult-friendly 'slice of life' anime, just more incongruous-seeming because of the 'pony' thing.
A lot of people in or around tech are furries, are into things like japanese animation, or are into My Little Pony. I don't consider myself one, but people often jokingly say that furries run the Internet.
And it's not really specific to HN. For instance you have well-known people in the community who do vaccine R&D, or cryptography, or contribute to the C/C++ standards at ISO, or several other STEM things that are pretty outspoken about their interests.
This is made more obvious on Twitter, where people tend to blur their personal and work identities a lot.
Twilight Sparkle's voice is indispensable in getting emotional contextualizers to work properly. The logo and profile picture is an homage to that fact.