Deleted huge files. HD space still filling up

OK everyone. So I needed some room on my Mac Studio. I had 30GB left. Moved @120GB to an external Thunderbolt Drive. Deleted files, emptied trash. HD space went up to 130GB available. 5 seconds later, only 65GB available. There's not even enough room now if I wanted to move the files back form my Thunderbolt drive. Makes no sense. Not running Time Machine or anything. How did I lose 60GB of space in an instant? Where did it come from. Killing me.