That does make me wonder where that phrase comes from, but I personally like it when people wish me good luck, because then I can blame the outcome on luck.
An atheist is someone who has no believes in deities. I know of atheists who believe in reincarnation, astrology and conspiracy theories. A more general term for someone who does not believe in any supernatural phenomenon is naturalist, i.e. someone who only accepts natural explanations.
That being said, believing in luck is believing in supernatural and is not naturalistic. We naturalists must fight every day against natural instincts to perceive agency when there really isn't one. I try to fight all thoughts of fate and luck, which try to creep into my thoughts. The more of these silly thoughts we accept, the easier it is for others to creep in. There is no luck, there is only probability. Sometimes things happen to our advantage, but usually they don't unless we are constantly trying to set the odds on our side.
So, really, luck is just how well a particular being faired in the game of chance.
We could not say the world was lucky I was born, just that I was lucky I was born. In this case, luck is just a statement of amazement that, for once, chance went in my favor. When you consider luck in the same way a gambler views luck, you are making a statement about probability. If you wish someone good luck, you are implying that you or someone or something can control the outcome. Really, when you wish someone good luck, you are just saying, "I will be happy for you if chance happens to your advantage, "
although, I admit that does not sound as supportive as good luck.