I agree with your initial reaction to both.
The First Answer was a comment/diagnostic question. It was not prasedphrased as an answer, nor posted with the intention of being an Answer (proper). It should have been moved as it was. Now if that in fact turns out to lead to the problem (in this case duplicate MAC addresses) then someone can post that as an Answer, which could be accepted.
Yes Mods can respond to any flag they see, it's not assigned to any one particular mod, just whoever sees it. Same with Edit Suggestions. I've run into one where someone edited a wiki entry I made; I didn't like their edit to 'my' content; I thought long and hard about that one before making a decision.
The Second Answer is a non-answer. IIRC they specified for nginx to listen to an IP the server doesn't have, which will return "unable to bind to port" (because you can't open a port on an IP that doesn't exist...). It's very hard to get the drive-bys to accept an answer or give more detail (SF has one of the lowest accept rates in Stack Exchange) so the mods are hesitant to remove an accepted answer, even if it is invalid.
"rejected" works, I can't think of a better word; and it's just fun to say too, like "guacamole".
