I am not a lawyer and this is not legal advice.
You're Right to Think There's a Problem
These screenshots might be easily recreated, but they don't constitute a short excerpt from the source. This is pretty clearly a substantial amount of material. Furthermore, their purpose is to provide a source (an Ask Ubuntu answer) that exists as an alternative to the original source, which could be seen as competing with or replacing it. There's not good reason to think this falls under fair use.
Unless the editor is the author of the blog post (in which case, we require disclosure for unrelated reasons), or has permission from the author, there is probably a copyright problem here. There does not appear to be any blanket permission or compatible license statement at the source website to indicate that the pictures could be used.
In addition--though this is not primarily related to copyright--even if the screenshots could be used, the current attribution is better than nothing but not great. When a reader sees a source listed (even if it's the only source), they don't assume content is directly copied from it, unless that is stated or the content is quoted. Some indication that the images originate from an outside source should be added (if the images are kept).
You suggested the images are easily replaceable. If it would be easy for you to replace them, that might be the best solution to this problem! (You are, of course, not under any obligation to contribute images for this purpose.)
In any case, given these problems, it's almost certainly best not to approve the edit at this time.
Theoretically, I could imagine (not being a lawyer and nothing in this post being legal advice) that the creator of the images might not have standing to enforce the copyright, due to the images being composed primarily of elements from user interfaces to which s/he does not hold the copyright.
I could imagine an argument that if it's fair use for the blogger to use the screenshots, then it's fair use for us to use them too (even second-hand).
This is a reason (among many others!) for us to avoid jumping to any conclusions about the law, and to avoid accusing anyone of breaking it. But this is not a good reason for us to have those images here. Unless someone who can actually give us legal advice does so (which seems rather unlikely), this is just one legal theory among many.
Plus, our goal is higher than simply being in a situation where we'd probably win a court case. We want all (or as much as possible) of the material here to be clearly non-infringing, so that as our site expands and as other sources are created based on ours (in accordance with our license), nothing has to be carved out later in response to a complaint.
Oli's answer to Should an answer that is a link to the answerers personal blog be flagged as spam?