Its possible this story is made up but I did know someone who stayed with a man who was arrested for having images of CSA on their computer.
I'm suspicious of the motives for publishing it, I think it's trying to move the overton window on CSA; it was only a picture, one he sent himself, he didn't have pictures of children on his devices, his pregnant partner stood by him etc. The pregnancy detail is an important part of the story in terms of manipulating the readers perception, you would expect a pregnant woman to be highly protective of her unborn child but here we are presented with a woman who, once she knew the details, stood by her partner. We're being persuaded it's not that bad, why?
I don't think the police have manipulated someone into committing a crime, they don't create fake profiles on gardening forums expecting to catch paedophiles so clearly this man was visiting sites where he was likely to find young girls to make contact with. That is not normal or appropriate behaviour for a grown man. If he made a mistake you would expect him to navigate away as soon as he realised. The intention existed before he made contact with the police officer acting as a 12 year old.
If this story is true then I think the woman will be in for a shock when it reaches court, all of the messaging details will come out and it would be surprising if he hadn't requested photos in return, sending photos is usually just a way of building trust and normalising the exchange of explicit images.
I could not stay with anyone who had done something like this and I feel for her daughter, she will surely find out why she can't live with her dad at some point in the future.