Quite many secular people, and even many Christians, have the misconception that the vast majority of Christians are fundamentalist biblical literalists. In other words, that they hold the position that every single story of the Bible is literally true as described, and should be interpreted as such, rather than being eg. an allegory or parable.
This notion isn't actually true. In fact, the fundamentalist literalists form a minority among all of the world's Christians (even if we count only those who consider themselves believers and who actively practice Christianity, rather than being "Christian" in name only but are in practice as secular as any atheist.)
For example, the biggest denomination of Christianity, Catholicism, is not a young-earth creationist denomination, accepts that the universe and the Earth are billions of years old, and considers the events depicted in the book of Genesis to be more or less allegorical and figurative. While individual catholics might themselves be biblical literalists and young-earth creationists, the vast majority accept the official position of the Catholic church.
Many, if not most, of the protestant denominations also have no problem in accepting the old age of the universe and consider the first chapters of the Bible more or less allegorical.
So why does one easily get the notion that the vast majority of Christians are fundamentalist literalist young-earth creationists? This is most probably because this minority of Christians tends to be the most vocal as well, and the subgroup of Christianity that gets into the biggest and most visible fights with secular people and the ones who most vocally demand special privileges at a governmental level. All the non-literalist non-fundamentalists are much more "moderate" and do not tend to be so vocal, start fights and demand special privileges and changes to law.