I can sure if that was the Mine-Imator it self. I mean MI is Running like a Movie when you're Not watching, or watching it. So I think this is because The MI software is designed to be a Game, but Animator type version. Remembering that MI was made out by GameMaker Studio 2 Engine, And Like it's name Gamemaker was designed to be a game Maker Engine. So MI was made by Gamemaker engine that makes Mine-Imator Software Became A Game.exe Program. So when Windows read it as a Game Program, Windows will Automatically Set the Mode into Default,Or Not Sleep mode. So maybe that's why It was not sleep mode.
Hope it will answer your questions.