The word 'delusion' simply means to believe something that isn't real. If there is no god, then all believers are delusional. It's not meant to sound as offensive as it probably does, though. Heheh.
Now, back to the guy saying that his god spoke to him. Let's say he believes his claim is true. Now, there are only two options left, since we know he isn't lying. It's either true... or he is simply imagining it (i.e. suffering a delusion). In order for it to be true, his god would have to be real. Proving that his god is real (or already believing so) is required before believing that he spoke to his god. Same goes for the other several million people making that claim.
Now, to be realistic... most people do not claim to have literally heard the voice of their god, or to have actually seen him, or what have you. Most believers see and hear god in things that happen in the world around them. They interpret these things as messages from and/or evidence of their god's presence. So, when they say they have 'personal experience of god', they only believe that because they already believe that. It's a self-sustaining delusion.
Now, back to the guy saying that his god spoke to him. Let's say he believes his claim is true. Now, there are only two options left, since we know he isn't lying. It's either true... or he is simply imagining it (i.e. suffering a delusion). In order for it to be true, his god would have to be real. Proving that his god is real (or already believing so) is required before believing that he spoke to his god. Same goes for the other several million people making that claim.
Now, to be realistic... most people do not claim to have literally heard the voice of their god, or to have actually seen him, or what have you. Most believers see and hear god in things that happen in the world around them. They interpret these things as messages from and/or evidence of their god's presence. So, when they say they have 'personal experience of god', they only believe that because they already believe that. It's a self-sustaining delusion.