It's realistic. Most law enforcement officers only have a high-school diploma. It isn't unreasonable to think that they would think that "Eliminate the State" was some kind of anti-american anarchic slogan, or that "Hash" was referring to concentrated marijuana...

Cops are a pretty stupid bunch. Not all of them, but quite unfortunately the majority of them...

Previously the U.S. government enjoyed conflating cryptographic algorithms with munitions.

See http://cr.yp.to/export/status.html

Maybe they were thinking (light heartedly) that a practical post-quantum signature scheme might raise the attention of the government again. So they're giving a shout-out to the legions of governments officials that might find themselves on that page once they whip themselves into a panicked frenzy.

The page has an anarchist-style logo in the upper left. I suspect that this, in addition to the normal stereotyping of "the authorities" as being clueless with regard to technology, is what led to the jibe.

I think it is a joke. The authors are probably anarchists.