Perhaps it's actually correct, but our intuitions about ridiculously long periods of time aren't good. Note that heat death is in ~10¹⁰⁰ years, whereas this Boltzman body would take ~10^(10⁶⁹) years. That second time period is literally incomprehensible. So we think, of course a fully formed human body wouldn't appear; in practice, that's not how it actually works; the fact that it appears possible is at best a mathematical artifact, not reality. But we're talking about a timescale that's not just longer than the age of the universe, or than the total lifespan of the universe, not just orders of magnitude longer than those times, but on a completely different scale. Given that, I think we need to toss out those intuitions.
As to the author's last question of whether such a thing even makes sense at all given those time scales, I don't see why not. After all, once the universe reaches heat death, as far as we know nothing from the outside is going to come along and garbage collect it, so why couldn't it last for an arbitrary/infinite number of years? And compared to that, ~10^(10⁶⁹) years, or ~10^(10^(10⁵⁶)) years, or whatever, is nothing.
As to the author's last question of whether such a thing even makes sense at all given those time scales, I don't see why not. After all, once the universe reaches heat death, as far as we know nothing from the outside is going to come along and garbage collect it, so why couldn't it last for an arbitrary/infinite number of years? And compared to that, ~10^(10⁶⁹) years, or ~10^(10^(10⁵⁶)) years, or whatever, is nothing.