Last I checked they were using the native Android scrolling physics. I could be mistaken though.
If so then I don't know why it has felt so different to every other app on all 3 of my Nexus devices (currently the 6P).
I guess it depends on the phone. Scrolling is smooth on my HTC One.
It's definitely smooth. Too smooth, in fact. It feels like my finger is slipping on the screen. No other app does this.
Glad I'm not the only one - I love everything else about the app but, as you said, it scrolls differently to every other app on my phone. So frustrating. Sticking with Chrome for now.