I'm pretty sure this is why your edit was rejected:
To explain a little further, I was confused that This edit introduces spam, defaces the post in some way, or is otherwise inappropriate. was chosen twice for the rejection reason. This reason is usually only picked when actual spam (or something that looks like spam) is introduced to the post or it is otherwise defaced.
Your edit did not look spammy. At best, I considered it an unnecessary addition to the post where the benefit is debatable but it definitely didn't look like spam.
From my personal point of view, I would have skipped that suggestion. It seemed hard to judge and I didn't realize the problem could be behind the link.
In general, I don't think Super User is less welcoming regarding suggested edits than other SE communities. Hopefully, after this misunderstanding, you'll agree.