You can sometimes get the reason by being a moderator/owner of a stream by looking at the flagged comment.
"_____ flagged _____'s comment" the word comment should be highlighted as well as the names, and you press the word comment to get to the posts comment.
As a fellow moderator around imgflip who owns and moderates lots of streams, it is a normal duty to check for false flagging, false flagging is when an user falsely flags an comment that does not break any rules within the stream and imgflip guidelines but is still flagged for a false or incorrect reason.
Correct flagging on the other hand are comments that do break imgflip guidelines and stream rules, if a link in a comment leads to an inappropriate site- such as sites with gore or nudity. Any comment with pure harassment or such also breaks the rules.
But it is important to check the context of a comment, perhaps if the image on the post the comment was on explains context.