Wonder why the results vary so much. Wait a second, I just re-ran the test on the default Android browser. Were you two using it instead of Chrome? It loads slower and lags at a few points in the scrolling. Actually, seems to scroll faster, too, in a way that makes site less usable. Could be a browser, rendering issue if you're not on Chrome.
https://news.ycombinator.com/item?id=11764257
I tried to replicate your and other commenters experience. I found issues on Android's default browser that didn't exist on my first, Chrome test. Did you use default browser or what browser you on?
Interestingly, I did not see any horizontal scrolling when I tried in Chrome browser (Mac OSX 10.11.4) in regular user mode. But on toggling device mode (in dev tools), and selecting one of the mobiles - Galaxy S5 or Nexus 6P, the horizontal scrolling started to appear, and it is a lot worse than on my actual android phone.
I haven't yet been able to identify the element that overflows, but the <html> and <body> seems to take default 100% width and are expected to be contained within the browser frame. There is some other rogue element, somewhere nested inside, which is causing this unwanted horizontal scrolling.
Thanks for pointing out this mobile testing methodology. It really helps to evaluate new CSS frameworks, which we see often nowadays.
Means it will run like a McLaren F1 on the modern stuff with almost no resource requirements. Ironically, it didn't matter all that much on desktops and servers. The new trends of mobile browsers and pay-per-CPU-or-whatever clouds mean it brings more benefit than ever. Especially at scale.