if this is 100% safe then why am I getting a virus warning
It's a false alarm due to some of the game files using crucial windows features. In your antivirus, there should be an exclusion option in which you can select the game's folder to fix the interruption popups. The only thing that this game changes is the wallpaper and a one time logoff event. If you don't want the logoff event to occur, you can disable it by going into "A Dark Place/Data" and deleting "SlientNightmare.bat".