As far as I know, “zeu” is any god, while “Dumnezeu” is the Jewish/Catholic/Orthodox God.
Why couldn't "Zeul lunii" refer to "the god of the month?" Doesn't "lunii" mean both "of the month" and "of the moon?"
It most certainly can. I just lost a heart for that and I'm a native speaker, it didn't even cross my mind to go for the 'moon'variant until after hitting enter. Goes to show you shouldn't rush these quizzes. The way you would distinguish between the two is, unless it's contextually more specified, assume it's the god of the moon. (i.e. March is the first month of spring. The god of the month is Mars in the Latin pantheon / Martie este prima lună a primăverii (/de primăvară). Zeul lunii în panteonul latin este Marte).