Just to clarify, it is not impossible to have a micro guppy fry, it has happened to me and it was in fact a guppy fry, I don't know, how it lived, nor do I want to know.
I was trying to edit my previous reply, the normal sized fry is in the rocks and the micro baby is on the pink cave on the left. That little guy is way smaller than his siblings and in fact now a less than a half inch long while the others are over a half inch long if not longer