Well, it doesn't sound reasonable to me. 2 years sounds like 'pretty much total beginner' level. No-one will be a good jazz player after so little time, and I doubt their brains would be those of jazz musicians with decades of experience either.
I agree that people need SOME time to learn the ropes but with proper training, 2 years is enough to be good. Note that proper training doesn't mean practicing certain technique, scale or etude hundreds of times. Nowadays there are systems designed over the years by schools such as Berklee effective enough to make someone a good jazz musician within 2 years, similar to many athlete training systems. No system can make legends, but decent musicians for sure.
Also, I don't believe in "proper training". I believe in learning from the recordings of the greats, and from playing music with people. Sounds like that's how Joey Alexander learnt[0]. I believe that, like many things, jazz can be learnt but not taught. Someone trained in some system will sound like the music equivalent of the academic artist - expert at following someone else's rules, but nowhere as an artist.
[0]https://en.wikipedia.org/wiki/Joey_Alexander
edit: Most people who go to Berklee are already pretty good when they get there, aren't they? Hardly starting from scratch.