IMO,

The dictionary is clear - does NOT include explosives.

Where the confusion comes in - is explosive devices - here it is, chemical, bio and nukes are explosive devices. And so is bombs.

Maybe the (key word) here is "wide spread"
You maybe able to blow up a whole building or a city block - but not the whole city like a nuke would.

The clarity would be is to place a human figure on it like say if over 5,000 people are killed than its a WMD ? ?
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