I'd stay away from talking about a "real" atheist the same way it also doesn't do any good to talk about a "real" Christian - you move into No True Scotsman range.
What probably happens, if people are atheists and 'convert,' is that they weren't rational thinkers to begin with and were either looking for something to believe, had a personal experience that they find too powerful to explain away, or already had a propensity to believe in things anyway and one of the major religions fit the bill. I've certainly known atheists who fell in with new age things rather than organized religion. Crystals and vortexes are just as bullshitty as Christianity, and yet atheists fall for that stuff all the time.
So, conceivably someone could have been an atheist and swayed by an experience.
What probably happens, if people are atheists and 'convert,' is that they weren't rational thinkers to begin with and were either looking for something to believe, had a personal experience that they find too powerful to explain away, or already had a propensity to believe in things anyway and one of the major religions fit the bill. I've certainly known atheists who fell in with new age things rather than organized religion. Crystals and vortexes are just as bullshitty as Christianity, and yet atheists fall for that stuff all the time.
So, conceivably someone could have been an atheist and swayed by an experience.