Take for example someone saying that they saw colors appearing in the sky, long lines of red, blue, green, and yellow! Now, most of us have seen a rainbow, and would be able to figure out that that is what it was. But, there may be someone that has never seen one, or heard of one, so to them it may seem "metaphysical".
There may be scientific phenomenon that happen only very, very rarely, that only a few people have seen, which may be next to impossible to replicate in a lab, but they still do exist.