I was annoyed to see the same mistake in this article (and its headline) when it first went up. They've since corrected it, but you can see the note at the end.

http://www.nytimes.com/2014/09/14/us/police-armored-vehicle-...

It's not a huge stretch to conflate the category armoured vehicle with its sub-category tank. Normal people aren't into browsing Wikipedia articles about weapons.

Its the same thing as the attempt to label main battle rifles and sniper rifles and deer hunting rifles as "assault weapons"

So if you don't like what he did, its a tank.