I suspect actually that the author adhered about as closely to "lean startup" as many self-identified "lean startups" who have succeeded in the past, and made a pretty average number of mistakes in the process. I don't think of 'lean startup' as a way to guarantee success, I think of it as a way to fail gracefully if you don't succeed. The author came pretty close to this, actually - it doesn't sound like they burned through enormous piles of venture capital money, it seems like they learned a lot in the process, it seems like they didn't spectacularly fail to make payroll causing half a dozen family-bound engineers to suddenly lose their livelihoods. The only less-than-graceful element of their failure was that it took two years, which is probably a little (though not a lot) on the long side. Frankly late in the process they came pretty close to scoring what sounds like it would have been a pivotal investor, and that combined with lessons learned could have produced a true MVP, product market fit, and a viable startup...
So, I think the author successfully followed a good chunk of lean software advice, made some mistakes, got unlucky, and failed. This is what most startups do - even most lean startups - and there should be no shame in it. Paul Graham himself has remarked he wishes he were able to bring himself to invest in more likely-to-fail black swans because that's the way you get to own enough vol to have a real winner in your portfolio - we all should be more comfortable with the risk of failure.