Unfortunately if someone who was once religious can lose their faith then someone who was once atheist can also find faith. I went from being atheist to having faith (although it was a very brief period and my ''faith'' was pretty weak since even though then i was still doubting and questioning it) back to atheist again. It was during that brief, weird period when i had started to believe that screwed me up more than i was before because when i started to research christianity more and spend time around christians and visiting christian forums that i realised it was much more abhorrent than i originally thought. There was a forum for baptists i visited which was particularly vicious and i realised i was never going to agree with their horrific views and that i had had a temporary moment of insanity.
But i briefly felt happy and high originally when i thought i could ''feel'' god, its like being drunk without touching a drink. Religion is a drug and a placebo, the feeling of euphoria and of being close to god is in the believers head the same way that the brain feels good when you drink alcohol or take heroin. I understand when people say they ''feel god'' and become addicted to religion because i felt this briefly, even though i came to my senses again fast. Christians are known sometimes to have a crisis of faith which they sometimes get over and find their faith again, other times they lose it completely and it never comes back. I had a crisis of unfaith which i got over again but some people don/t and lose the unfaith for good.
Anyway in conclusion some people who say they used to be atheist's and are now christians will be genuine.