I agree with the owner in that FOF made a really pitiful mistake. If it had been a tiny kitten, gender is harder to check, yes. But an older cat should be obvious even after his testicles have been removed. Be more careful and pay for a check up. Given the state of their goof, she is perfectly reasonable.

Beyond that, I do think that Roy's owner should hold the responsibility. A friend of mine once caught two stray cats out of a colony of ferals. One was very friendly, the other was not (although she's perfectly wonderful now that years have passed). Friendliness does not equal owned.

There are safe ways of letting a cat out yet keeping them in YOUR yard. There are different types of safety collars that you can give your cat. One of mine has one that stretches considerably when hung, but lays tight on the neck, otherwise. It doesn't have to break away, and the cat will always be able to get out if she pleases. It also rests snugly enough when she scratches and plays that she does not wriggle out of it. This might be Roy's ticket.

I think it's ridiculous that people only blame the FOF or claim that it's unreasonable to request that people keep their cats in their own yard. Use a little creativity!! Chicken wire is cheap, all weather netting is cheap. You could section off a good 500 sq foot of yard for around a hundred bucks. Do this near a window and attach a cat door to an old AC shell, and you have an excellent adventureland for your cat without breaking the bank. No need to keep your cat running around your neighbors' property.