Great excuse for bad spelling!
The creation of new words to express ideas isn't "bad." It's the natural evolution of human communication. There are plenty of words in common use today that didn't exist a thousand years ago. For instance, "telephone."
Yeah, still not buying it as valid just because someone made it up.
By that reasoning, no form of language would be valid. It all started with someone making words up.
Let's also not forget that the spelling "Numan" is a pre-existing word from before Phantasy Star came around. It's a real life name. Obviously it likely wouldn't have the same meaning, but it wouldn't be the first time a new meaning has been applied to an old word or name.