They're doing their job poorly, though. You can't go on a social media site, get called out for something and respond the way they have so far. I'm a 14 year comms professional and you either don't respond at all to these kinds of comments and just let it be (so it doesn't acquire more attention) or you formulate a measured response such as "This position's salary range is commensurate with the experience we are seeking within our budgetary requirements."

It's really that easy.