Heh. Yeah, good point. The most "NSFW" stuff you'll see is bras, panties, and I think you see nipples twice. And one of the characters uses a shower head to pleasure herself. I believe, beyond that, that's it. (EDIT: New update also sees an ass, so...) Seems like a waste of someone like SoulCentinel, but I can't say I haven't been enjoying the game all the same.
But yeah. It's marked NSFW merely for the ecchi content contained therein. If it weren't for those things, it would definitely pass as a SFW parody.