Play Store now checks modded apps to see if they're "outdated". If they are, they'll show up on the update list. In Obey Me's case, it's thinking that your mod is not the latest version when in fact it is. Google has just made it more difficult for modders in this latest attempt to force people to download from them & them only.
Still showing up on play store updates list after installing latest version. Google definitely has changed something there since many other modded apps show up as well according to many other users.