It might be as well if we were to define our terms before we continue.
A good place to begin would be with the word "knowledge."
Knowledge to some is limited to those things they can see and touch. A chair exists because they can SIT on it.
So when someone says they know God exists---without seeing or touching (at least, in any physical sense) Him that is NOT knowledge to a REALIST.
It is a belief...a faith...based upon certain chemical and electrical phenomena in the brain. To a Realist God may only be "a blot of mustard...a bit of undigested beef."
(to quote a certain Ebenezer Scrooge).
But to the person who has HAD the experience of God both it and He are as real as any chair. Because they have "touched and been touched" by Him. Not in the recognized physical sense---yet still it feels real.
There is a hymn which contains the words "You ask me how I know He lives? He lives within my heart!"
To a person of faith no other evidence is required.
To a Realist that is the goofiest thing they've ever heard.
It's not really goofy but it is...unhelpful.
Let's look at it THIS way...
Well, that was fun....now we'll look at it ANOTHER way:
The Realist says this "Experience of God" isn't real because it isn't based in MATERIAL REALITY.
It's a psychological event.
Yet they claim that a chair is real. But a chair isn't REAL either.
It, too, is a psychological event. Or, better, a PERCEPTUAL event.
We know that a chair is REALLY only a bunch of neutrons and protons and so on arranged in a certain order and moving at a certain speed. Not only isn't it a "chair" (which is the name we give our perception of these neutrons and so on) it isn't even "solid". There are huge gaps the arrangement of these (is it okay to use the word "particles" here?) I'll use it anyway. There are gaps in the arrangement of these particles---we can't see them (without certain aids to our vision) but they are nonetheless THERE.
All of this is true of OUR physical bodies as well.
In fact it is true of everything we perceive.
The only difference, then, is that EVERYONE can experience a chair.
NOT everyone experiences God.
But now let's ask ourselves how someone who hs been blind since the day they were born experiences a chair.
They can't SEE it. They can't admire the beauty of the carving or the colors of the covering.
But they can still sit on it.
So it is for those who haven't experienced God.
They can still enjoy the world He created. They can still enjoy the warmth of the sun and the beauty of a butterfly andf the sweet scent of a rose.
They just lack the sense that would open them up to the transcendent.