I'm guessing his thought process was along the lines of "Well he thinks the age of consent should be lowered, but he never actually sexualized minors." But if he wasn't sure he should've asked the site owner (u/magnora7), probably the only one who should be making such dangerous calls.

Also, the approval could've been an accident. I do that sometimes. The approve button doesn't have any confirmation, so it's very easy to hit by accident, especially on mobile, and there's no way to undo it. Anyone who's been a mod here or on reddit will probably tell you the same thing. I've actually wondered if reddit set it up that way on purpose so they can "catch" mods approving the wrong posts, and then use that as an excuse to ban them or the entire subreddit.