That’s backwards. One dose not have to disprove something to stop believing in it. One only has to loose faith in the evidence in its favor to no longer be convinced of the belief.
It’s not “reasonable to assume” that because one does not believe now, they never did. People process new information through life that leads them to new conclusions about may things, from relationships to politics, morals and ideology.
But to approach someone who left your ideology out of the blue like that and publicly accuse them of never being a believer is an arrogant and condescending act of disrespect, symptomatic of a defensive and reactionary personality. Not very Christian of you.
Looks ok to me...