He experienced a visual disturbance in his periphery manifesting as the false perception of a person

Which can’t be explained by an unfocused eye. They do a lot of speculating to come up with a reason why he could possibly see something out of the corner of his eye. But, that’s only the physical part of it. It doesn’t explain why he might think that whatever he was seeing was “a figure” and moved like a person.

That’s like saying that ghosts can be explained by wearing glasses with dirty lenses, then going into detail about how dirty lenses can cause someone to see something that isn’t there, while ignoring the elephant ghost in the room. Except it’s even worse because a smudge on your glasses causing you to “see something that isn’t there” is really easy to test and barely needs an experiment to confirm it’s true. But, low frequency waves causing someone to see something that isn’t there isn’t something that has been tested. It’s pure speculation.

So, pure speculation that low frequency waves can cause someone’s eyes to blur in such a way that the corner of their glasses is mistaken as something that isn’t there. No proof that has happened or can happen, just speculation.

Then ignoring the elephant in the room that just because someone might not see clearly if their eye is vibrating, that is somehow magically interpreted as a figure moving like a person, which they interpret as a ghost.

There’s a humongous jump there from “a certain frequency might cause the eyes to wiggle” to “and therefore that’s why he saw a ghost”.