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.