I'm sorry for the inconvenience of the experience. Let me explain the intent of the filter, though.
There are two ways to edit a question or answer. If you are editing your own posts, or if you have at least 2000 reputation when editing anyone else's posts, then there's no filter. You can perform a tiny edit, just like I did, without any cause, and it'll just be done. The only person doing anything is you, so there's no harm.
If you have under 2000 reputation, then you are allowed to suggest edits to a post. These suggested edits must be reviewed by another user who has at least 2000 reputation, who must choose to either approve or reject the edit. In this scenario, you will be requiring another individual to approve the edit, so we require a generally minimal courtesy for suggested edits - they must have at least 6 characters changed.
Yes, in some cases, it takes a single character to make a world of difference. This particular example, there is only one fix to be made. In the vast majority of cases, however, there is often a lot of other edits that can be added to such a post, and they each are actually pretty miniscule in impact. Yet whether someone is suggesting a substantial edit that fixes several typos or grammatical errors in a post, versus the addition of the letter "a" in a sentence, the required time to approve is the same. It's worse when, what was often the case in the early testing of this feature, people would make 1-2 character edits to fix one piece while ignoring seven other typos in the same post. Now the approver has to approve that and fix all the rest of the post, when a better editor could've just suggested it all at once.
Thus, we try to favor those edits that have a lot more content, in order to optimize the time of our users in approving these edits. We're aware that sometimes, like here, there is a remote case where truly, only one tiny fix is needed to make a difference. In the big picture, though, these cases are very rare, so in general the filter primarily hits only those who are indeed making actual trivial edits.