Well, most of the pokemon movies do not link to the normal anime most of the time. Only a few times has a movie been brought up in the series. When he said there was 150 pokemon, he probably meant only what Ash would most likely see. He probably knew that there was more than 150 pokemon. When he went to Bill's Lighthouse. Bill said there is over 150 pokemon and that more were discovered everyday. There was potently over 1000 pokemon on Bill's wall, but they only showed the ones we knew about in Kanto.