It doesn't mean the "liar" part, it means that if you were to say something like この嘘つき, you probably wouldn't translate as "this liar", but "you liar" (you could say that directly at the person you think is a liar).
I think the explanation given up there is "you ...". One casual/impolite example is "このやろう", which can mean "you (something impolite)" when contextually translated to english, depending on context and how the conversation is being carried out, sometimes people like to speak in 3rd-person context. Literally, it is "this (impolite reference)" e.g. "this bas****".
