EQV - Initially paleontologists had a few fossils to go on. Neanderthals were clearly hominid but not Homo sapien. More and more samples were discovered allowing scientists to say more about their anatomy. Sites where they lived and died were discovered revealing facts about their culture.
Then geneticists were able to recover some samples of DNA and it appeared that they never bred with humans. With improved techniques more of their genome has been decoded showing that we did in fact share some ancestry with them.
Science progresses constantly as new discoveries opens up new possibilities for research.
Your ignorance is not interesting to anybody. Read a book FFS!