There's really now way to know for sure how humans arrived on earth because there had to be some other species or something that evolved into humans.
But there were other species of animals on ear long before humans arrived on earth and it is possible that humans may have lived on another planet and somehow arrived on earth years ago.
But that would have been billions of years ago when humans got onto earth so unless you were there at the time there is really no way of knowing.
I believe myself that humans could be aliens of earth but not 100% sure on that.