Too much speculation and personal opinion

Wiki ate my post so gonna keep this as brief as possible. Lugh shows no real signs of godhood. He displays no God-like powers, he appears no more preternatural or supernatural than the average player and it can even be argued that a lot of players are far more God-like than he is. It could be that he became a God but there's no indication that he did whereas we're explicitly told how Mari became Nao (nor is it even suggested as to what kind of difference there was before/after attaining godhood. The claims that he is a god don't seem to match up with the rest of the game and as Morgant in G3, calls himself a human when talking to Ruairi ("And one more thing. I'm not a Fomor…I'm human. Just like you.").
The game establishes that Nuadha is a god. Everyone says, recognises and accepts this including other gods (and if we're to believe Lennox, Nuadha's title as King of the Gods is out of respect, not his actual position). It's not questioned, it's not made dubious, there is no room for reasonable doubt. Lugh on the other hand is almost never referred to as a god and having people claim/believe he is one doesn't necessarily means it's true.
As said (many, many times now), "[person] said [being] is a god" isn't the same as "[being] is a god".