Most online discussion sites (reddit and HN, for example) focus overwhelmingly on US politics. This is significantly less relevant for the billion-odd people who use the English language internet but do not live in the USA.
He didn't say anything about US politics - he specifically said anything 'slightly political'. Trump is an example of what happens when a critical mass of people adopt that attitude, and it could just as well happen in any other country under the right circumstances (and indeed has many times in the past).
Yeah because the Tea Party didn't exist under Pres. Obama. The Birth Certificate truthers exist, Alex Jones, Rush Limbaugh, Anti-Bush, and the No Blood For Oil crowds have existed forever across the spectrum. The only thing that's happened is that the internet has made everyone willing to turn everything into politics louder, less willing to listen, and easier to find an echo chamber. People talk about politics because it's the only thing that's literally relevant to everyone.