Untrue. There one can define all sorts of moral systems based on ... well, whatever principles one decides are important. "Might makes right" is one, for example.
The distinction is, rather, the what basis by which can one say "that is wrong," or "this is the right thing to do," and have it mean only one thing.
At root, the questions boil down to these two:
1) Do you propose that true "morality" is based on a set of fixed and immutable principles?2) If so, on what basis do those principles come into being?
It's at that point where one gets into the necessity of God, if one is to assume that moral principles are absolute, rather than relative.
I would disagree.
You can be in one of three states:
moral
ethical
legal
Without God you can not be moral, it maybe possible to be ethical.
Since ethics are in general based on morality it may not be possible to even be ethical.
So I believe without God the best state one can be in is legal.
The only true morality MUST be based on a set of external and objective rules.
Otherwise, your “ethics” are nothing more than your own personal interpretation of the truth of right and wrong, leading invariably to “situational ethics”.