While I'll admit this is a little bit of a grey area, in general I agree with your reject vote. The author of a suggested edit is never the same user as the author of the post (or it wouldn't be a "suggested" edit) so this sort of content in a suggested edit is never strictly appropriate.
What makes it a grey area is that sometimes it's blatantly obvious that the two user accounts belong to the same individual—ideally because they have self-identified as the same person but everyone has a different threshold for what seems "obvious" to them. This is why the system is designed in most cases to have multiple people involved in the review.
If we assume the edit is made by the original author on a new account, the only reason to reject would be to give them a slap on the wrist for creating two accounts. That's not really useful or appropriate, in my opinion—in the vast majority of cases, the extra accounts are a goof and/or one of them is unregistered (representing a first interaction with the site). In the rare case that this sort of behavior represents an abuse of multiple accounts, you'd want to flag for moderator attention anyway, making the suggested edit review a relatively minor issue.
In this specific case, I think the common identity of the users is fairly clear, and I might have approved the edit. That said, I have relevant tools you don't have, like the ability to check IP addresses. I don't think it's unreasonable for you to have voted to reject.