I’m sure it relies on users using the NSFW tag on their posts, which can be unreliable. I’d be ok with an option to remove the random section altogether.
I also noticed that even if you have NSFW content allowed, it correctly blurs the thumbnail when you are browsing the homepage or whatnot, but does not blur those sidebar 'random posts' and 'random threads', so you are just browsing your homepage and find a massive donger plastered over the right side of your screen.
So it seems like an issue of both not hiding it when NSFW is hidden and not blurring it when NSFW is allowed but blurred.