It was his laptop that was among the stolen item. He said he has the paper top of the laptop keyboard saying Bitcoin private key so he thought his Bitcoin investment was gone but when he checked it, the coins are still intact and he moved it asap.
Here is another link for the video : https://www.youtube.com/watch?v=ghG6Uv_j5Xw
The discussion are really funny, Mr. Beast is just lucky that Bitcoin at that time isn't as popular as today and the guy who stole his laptop has no idea what Bitcoin is or just in a hurry that it missed the paper that has the private key which is lying on top of his laptop.