Not if it's a God like the Biblical God. If that SOB comes down with chariots of fire and hordes of angels with trumpets, parting oceans and the like, there will be no doubt and no one will deny it.
Oh, I'd highly disagree that this wouldn't be met with denial by many that it is 'god.' I think it would very much be attempted to be understood as some sort of (physically) natural phenomenon. And if determined that it is not of this world, then likely determined it is of this universe with abilities that humans don't currently possess.
To me, it'd be like if any of us traveled back in time with any of the gadgets we carry today and/or awareness we have of current times. To people of long ago, we'd probably come across as gods, and supernatural in what we have with us. While to people of the future, we'd be primitive. One short step away from cave people.
Herein lies the difference in our opinions. Yes, I understand that the God/theist relationship is comparable to the parent/child relationship. I mean Christians call God "the father" after all. The idea that a God is looked on as a father or mother figure is understandable.
But a theist does not think their God and their parents are the same. There is a vast and robust difference between (take Christians for example) their parents who are merely other human beings with diminishing power over their lives that ends in the mid to late teen years, and Yahweh who is an all powerful deity with ultimate control over not only their daily lives but the fate of their eternal soul.
This is why we need different words for the two things, Gods and parents, and why I reject using the God label to describe a parent.
Some theists think what you are conveying. I am a theists that understands / knows human parents to be gods. Extensions of Creator God. With the only rational difference being that Creator God created the beings in human form and not the other way around. I get that an atheist actually holds the exact opposite assertion, that human beings are 'creator' of Creator God (as in making such a being up). A possible difference, though not exactly rational is that we as gods are not fully aware of our divine self. Yet, I find that very challenging to reconcile within reason, for it is possible that we all do know this at this very moment and that I may not be aware of that fact. Then again, I might be.