I was just joking around
You asked why I simply put a smiley face in my reply. Sometimes when I can't think of anything at all to say but I want to say something of a favorable nature, I just answer with an emoticon.
So just for fun when you asked me why I put a smiley face I replied facetiously with a sad face LOL. But that was really for no purpose.
Sorry for sounding totally confusing
For example, if someone makes a post that contains only a joke, I answer with a smiley face.