The problem seems to be related to the terms used.Indeed, a lack of explanation is just that, however a lack of explanation doesn't lead to an atheist position, but an agnostic one. To make the leap, you have to effectively say 'I don't know, so I think...' rather than just 'I don't know'. As I said earlier, simply lacking an explicit belief in gods is not enough to make you an atheist, weak or otherwise, using the generally accepted definitions. (incidentally, the same group of atheists who have tried to introduce this all encompassing definition of atheism as including anyone who doesn't have a specific belief in a deity also tried to redefine agnosticism to mean something other than 'the position where the existence of god is unknown, unknowable or irrelevant' to a claim about knowledge to be tagged on to atheism.)
Personally, I'd prefer no label.
If person A comes to me and says "I've been to heaven, but I have no evidence" - I'd simply not believe him because he has no evidence, also because it would require the suspension of the currently known (tested & proven natural laws of science), that's not the same as saying he is lying.
But this is not the same as simply thinking of this situation in an agnostic way.
As said, agnosticism concerns knowledge.
It's a pointless discussion really, as what's the point applying a label to somebody who doesn't take a position on a subject as they reject the notion entirely.
You don't assign a label to people who are non-Buddhist, or non-Christians, you either are or you are not.
I'd suggest watching a good video on youtube - Qualiasoup / Lack of belief in gods.