They appear to have change something in the past few minutes. When I first opened this HN thread it showed me Google's homepage. Now I'm also seeing that redirect.

You can just replace captcha.nsa.gov with www.google.com to see what it used to serve up: https://www.google.com/logos/2019/loteria/rc2/loteria19.html...

NSA has just shut down the proxy. The link was a Google Doodles game.