Just read the first paragraph of story and... I can't see any misspellings. (Pasting here, the spellcheck points out Samus, Aran, Metroid and "molted", which I thought was OK.) (E: ok, "futher" for "further".)
A couple of missed words or odd linguistic choices, but compared to the number of lines, not many.
The one specific misspelling that the tweeter points out is consistent throughout.
I was curious so I did the requisite short bit of scripting.
I think you're right, the misspellings are independent. For a few words (like "begining") the text contains the correct and a misspelt word. But for most misspelt words ("carefull" for example) the text contains only the misspelling.
Thus, the text being fully justified is independent of the misspelling.
I think it could have been written in something like MS-DOS edit, which doesn't have a spell check feature anywhere in sight. So it never saw a spell checker, they didn't have too much awareness of the errors. Maybe they also didn't care about spelling too much - thinking up words that fit in the spaces is fun but correcting spelling errors isn't much fun.
The document being an in depth write up of Super Metroid probably also says something about the person's character!
A couple of missed words or odd linguistic choices, but compared to the number of lines, not many.
The one specific misspelling that the tweeter points out is consistent throughout.