Edit, the author, Robin Sloan, is a fiction writer. That's... a little disappointing, but still it was a wonderful story.
It should have somehow been tagged as fiction.
Sure, it's right at the bottom, and "short story" is not entirely unambiguous, but I think most people would commonly use that phrase to refer to a work of fiction. I think I would have enjoyed it just as much if I'd known it was fiction from the start, but making that too obvious at the beginning may have removed a little of the charm.
The synth itself is real, however. Here's a video of someone much younger than Maisie making noises with it... https://www.synthtopia.com/content/2016/05/21/modular-synth-...