Maybe she walked in the room right as he said it?
Also, I'm making sure he isn't under plain drugs, only herbs. However, along with the hormone boost, there could be a different herb that causes an Amobarbital effect - a truth serum. Afterward, knowing that she heard him, he'd probably have to confront the issue, or face awkward silence for however long they're around each other. If she didn't do something under that situation, he'd have to.
Whether she'd agree with it or not is a different story, up to you, being her creator.
EDIT: I have to ask, since I offered to co-GM with Quto on this RP (Since he and I have been tossing ideas continuously at each other), if you'd have any problem with it?