I raise you,
When Muhammad (PBUH) said, "...for if one of you were to spend gold equal to Mount Uhud, it would not amount to a mudd (a handful) of one of them, nor half of it," that is obviously a lie.
Sure. But he was not required to make blatant false claims. If he said mustard seed is a very tiny seed yet when it grows it's bigger than trees bla bla bla the parable would be perfectly understood by everyone.
Why did he have to claim it's the smallest on earth?