Is it true that all whiskey is bourbon, but not all bourbon is whiskey?

No, it is not true that all whiskey is Bourbon. Bourbon is a specific type of whiskey that must meet certain legal requirements, such as being made in the United States and containing at least 51 corn in the MASH bill. Other types of whiskey, such as Scotch or Irish whiskey, do not meet the criteria to be classified as bourbon.