It could be someone mistakingly using a new account (in which case I'd approve), but if it is from an actually different user using the question for his own (similar, but not necessarily equal) issue, I would reject the edit as 'clearly conflicts with author's intent'.
There is just no way of knowing, so I have skipped the review.
These do come up occasionally. This is how I handle it (comments/suggestions welcomed).
I start with general rules that are independent of who the author is:
If it is non-substantive edits that improve the question, I accept them.
If they are substantive edits and I can't validate that they are correct, I skip them.
If they are substantive and correct, it depends on the scope. If they fix technical typos, I usually leave them as replacement text. If they apply only to certain cases, like newer versions of the software, or pretty much anything of a bigger scope, I re-edit if necessary to make it supplemental text. I add attribution so it is clear that they are not the original author's words. The author can always re-edit to incorporate the change.
If a substantive edit is from an anonymous poster, it gets a lot of scrutiny. I usually reject it unless there is clear and convincing evidence that it is correct, in which case, I follow the above guidelines.
If the edit under a different username appears to be (or claims or implies to be), from the OP, I add to the above guidelines.
If it is apparent or probable that it is the same author (like that question), and the edit doesn't conflict, I'll accept the edit as if it's from the OP, and leave a comment on the question alerting the author to the potential need to roll it back and advising them to get the accounts consolidated.
If I'm not confident that it's from the same author, I treat it like any other edit but add a comment to the question as above.
If the edit conflicts with the original wording and the poster implies that he is the OP, I generally reject it and add a comment that those kinds of changes need to be done under the original user name.