This means to dismiss an argument based on where it came from, or rather who is making it. So on a forum people might swap dating tips or advice, but then advice or an argument is discounted because it comes from someone who is single (although the advice is possibly good). I think this is why a lot of online forums that should really be positive and results focused end up being negative echo chambers. People can perhaps be objective in seeing what others need to do to change their situation easier than seeing this for themselves and their own situation, but perhaps don’t feel qualified to give advice — which is a shame as anyone can have common sense.