People are confusing a lack of belief in something with disbelief in something, I think. If you never heard of (whatever), you have no reason to believe that (whatever) exists. If you have heard of it, but do not believe it exists, then... you disbelieve in that (whatever).
Until I typed this, I had never heard of green and purple gorillas, so I did not believe in them. Now, of course... I do.
Until I typed this, I had never heard of green and purple gorillas, so I did not believe in them. Now, of course... I do.