As Caroline drifted into her sleep, she didn't know that her assumption was spot on, except Amon did fool around with her a little.
When both of them were inside their office, Amon could smell how horny Caroline was and he knew that as soon as she leaves, she will pleasure herself or wait for her husband so he decided to play with her mind by implanting a thought inside her head.
When she haves sex and is enjoying pleasuring herself, she will think about him, it was a simple mind manipulation that made Caroline think about him during her most pleasurable moments, and luckily for her Amon didn't make this permanent as he felt it would be too potent for a human such as Caroline.
