This is absolutely a backdoor - there is no other way someone would be able to perform such actions server-side. In the studio of your game, hit CTRL+SHIFT+F and type require, this will show you if there are scripts in your games requiring potential backdoors. Note that not all requires are bad, as legitimate systems such as your Adonis admin also use it.
I’d also make sure that you have a legitimate copy of Adonis, if you’re using one from anywhere other than this model remove it immediately: Adonis Loader [Sceleratis/Davey_Bones] - Roblox