Yes. Edits that add image descriptions (or in this case provides a transcript of text in an image) add accessibility without changing the core content of a post and should be accepted.
That said, this particular edit has been accepted, and it appears that the reject vote was a simple mistake.
No, such an option does not exist. Once you finished reviewing an item, you cannot change your decision. Don't worry, mistakes like this happen; that's one of the reasons two approvals/rejections are necessary for a final verdict on the edit.
With the migration to CommonMark as of June 2020, you can now use three backticks to denote a code block. This more explicit format leaves no room for the renderer to have to guess whether your spacing is part of the list or part of a code block. For example:
- List Item 1
This sits between 2 list items, but is not indented so it is not ...