The first definition line comes from a definition of a weapon of mass destruction as related specifically to criminal terrorism charges in the US federal code.

The first definition line comes from a definition of a weapon of mass destruction as related specifically to criminal terrorism charges in the US federal code. In this case they are basically setting the lower bound for what could be classified as a 'bomb'. Nothing more. The WMD definition you are probably thinking of (and the one which is more relevant to the original article) is the military definition outlined in various conventions and treaties.