Say I placed you in a dark room and I ask you to make mental note of anything you feel or imagine. Everyone hour I turn on the lights and you write your observations down. This is being objective in the first person, to data, only you can experience. Another person may record different things that do not match. They are also being objective in the first person.
To examine the first person's evidence, the second person could (should) create tests that are
designed to falsify the first person's evidence. Granted, not easy to do, since things may have changed - such is the nature of subjective phenomena. Nonetheless,
only if the first person's observations
cannot be falsified should we consider that the experience might merit further investigation.
Unfortunately, since there is no way to test SB's experience, there is also no way to falsify it. Which means an hallucination (or merely an overly-enthusiastic interpretation) cannot be ruled out - by objective observers - as an explanation.
As you point, out, person one could have hallucinated the whole thing. If so, while he may still have experienced things, we would be to rule out an objective existence of such things.
The
objective existence of heaven is what were after here, not person one's - or SB's - subjective experience. No one here is challenging that SB
thinks he experienced heaven.