Exactly, there is no sexual content being shown at all. The plug in question is barely even shown, there is no pussy juice and her face is only showing a mild blush. She's not engaging in intercourse, nor does she have any kind of Ahegao face and her panties cover everything up.
Although it's not explicit (so the wiki probably does need to be updated), object insertion is mentioned under questionable as one of the items not allowed under questionable, although it does mention it in concert with BDSM.
As for where object insertion should go in regards to rating, I propose to move that coversation to topic #8495.