Disclaimer: As a non-parent, my words should be taken with a grain of salt.
If I were Leslie, it wouldn't be the sexual curiosity that worried me. It would be the trouble you can get to surfing pron sites and the lying. You guys may have sites you go to that are free, that don't attempt to download spyware/adware/viruses, and you know when enough is enough. But can you trust an 11 year old with that? She's being a good parent by monitoring what he's doing and where he's going and not being an absentee parent that everyone here admonishes. She tried to talk to him about it and he lied, another bad sign. Yes, I think an open line of communication is key but isn't he the same boy who took her hand cream and lied about it too? The open communication may be out at this point, so monitoring is the next best thing.
With all the ways a child can find trouble online, sexual predators and such, she should be preventing him from surfing when she can't be around to know what he's doing and where he's going. Not to mention the hours of sleep that he misses that will cause issues if that's allowed to continue too.
It's not the end of the world, but at least she is in the know, so she can decide what is healthy curiosity and what it detrimental.