They are some set of people in this earth that doesn't have any specific religion, and while some have but it doesn't follow the ways, but God is aware of all this things. Those people can't say that they don't know that God exist.
God revealed himself is different means which we can imagine through the beautiful things he created and also making sure we are alive everyday. This means that even without religion, people can still have some awareness of God through the world around them and their inner sense of right and wrong.
The Bible also calls all people to come to a deeper knowledge of God through faith. It presents the idea that a true relationship with God is more important than simply identifying with or without a religion. So while the Bible acknowledges those without religion, it encourages everyone to sincerely seek God and build a personal relationship with Him.