We can attempt to deduce the point from the comment. The only assertive statement that the comment it replied to was "close to" the stupidest, but not the stupidest.

One possible evidence for that sort of statement is presenting the actual comment that is the stupidest, but such evidence was not presented explicitly.

However, we can assume that the author intends the justification to be self-apparent; with this assumption, the best explanation is that their comment itself is the evidence they wish to present, ergo the actual stupidest comment.