Our policy is very clear: greetings and salutations do not belong in posts. People are encouraged to edit them out whenever they come across them.
Now, I realize you're saying you didn't know about this policy and that now that you do, all of your posts comply with it. That's great. And it's totally fine that some of your old posts didn't. We're not punishing you for it. We don't even necessarily expect you to go back and fix all of your old posts. Better, other people can do that for you, without you having to lift a finger. It doesn't hurt you in any way to have an edit made to one of your posts.
So we know that the edit was valid and correct. The only remaining issue, then, is whether this edit counts as "too minor". The problem is, that's entirely subjective. Apparently 3 out of 4 reviewers thought it was a significant enough improvement of the post to approve it. Even if they were wrong and it is a minor edit, I can't see what harm was done.
And yes, it is possible to roll back an edit. But that should only be used for cases where the edit is truly inappropriate. For example, when the person has vandalized your answer, or completely changed the meaning of your contribution. This would not be a legitimate usage of a rollback. Even if you were seeking vengeance against the editor, it wouldn't have that effect. His edit was already approved, he already got whatever imaginary points from it that he's going to get, and your rollback would just count as an additional edit.