Sounds right to me, and as I say, one needs to be careful with that or the next thing we know we are going after the Pope because God told us too, or something fanatical like that, IYKWIM.
As far as the OP goes, it could be as we familiarize ourselves with God, as you were with your software and me the woods, we see so many things sub as well as consciously that might be perfectly viable proof but if someone asks us what proof we have, we may not be able to tell them, but we have it nonetheless.
But in the end, I just don't know enough about it to say anything is fact one way or another in that area, but not being able to answer the OP's question or that we may not know how we know how we distinguished the difference between delusion and belief, doesn't necessarily mean we cannot, or that our belief is delusion.
The OP does after all strike me as trying to tell us if we can't answer the question, our beliefs may well be delusion. It's what he thought was a good Christian stumper/faith killer...something he wishes we'd buy but regardless of what we know or not, I seriously doubt he's going to sway anyone to concern themselves in the least over their beliefs being delusion. Thinking he could would be his own little delusion.