Are all atheists this ill-informed about religion?

[abaris]

Many atheists became atheists because they read up on the Bible.

Yes, but they mean listening to their pastor/priest interpreting what they have to believe. So much so that evangelicals often deny catholics the status of being christian. Which more or less answers the OP in a nutshell.

There even was a time when the church didn't want laymen to read the bible in it's entirety. Can't be bothered to look up the particular regulations right now, but all through the Middle Ages, only certain parts of the bible were fair game for everyone. Reading and talking about anything else, was frowned upon and led to be burned at the stake a few times.