First of all, your edit is totally legit (thank you!), and it should have been approved.
The edit was rejected because 2 of 2 reviewers voted so, and by the powers that be (the Stack Exchange software), that's enough to reject a suggested edit.
Your next question might be why did those 2 users vote to reject? Only they can answer that.
But I'll venture a guess that they simply haven't seen the comments between you and the author.
Had they seen the comments,
it would have been clear that the change is approved by the author,
therefore it should be accepted,
and the reviewers would have voted to accept.
It seems that on the review page of a suggested edit,
the comments are not visible.
Reviewers must manually open the post to see that.
That's a bit of extra work for reviewers.
Especially when there are in fact no comments on a post,
but to avoid false positives like this one,
reviewers are forced to systematically open every post they review before making their decision.
I think it will make sense to post a feature request on https://meta.stackexchange.com/ to include comments on posts in the Suggested Edit queue, for everyone's sake,
if such request doesn't already exist.