That roommate was a separate person. As described in another comment, he tried to set a timer that would not cook anything, only start beeping in thirty minutes. Instead, he set the microwave to run - which is to say, cook - for thirty minutes, which melted the non food item inside the microwave.
Are you that roommate? Or are you saying he tried to set it for 30 seconds?
Neither.
That roommate was a separate person. As described in another comment, he tried to set a timer that would not cook anything, only start beeping in thirty minutes. Instead, he set the microwave to run - which is to say, cook - for thirty minutes, which melted the non food item inside the microwave.
I apologize for the ambiguity of my phrasing.