That's wierd. If auto ration is disabled at the Android system level I don't think it's possible for an app or a web page to overide that. Are you sure auto rotation is off in Settings or Quick settings?
I've got Rotation Control on my Android phone and kbin.social doesn't rotate when you've got it set to a fixed position. (It's an app I got through the Google Play store a long time ago.)
There's no app yet, but there is a Progressive Web App (PWA) which is like a website in its own app. If you use Chrome, you can get the PWA by going to kbin's front page, open Chrome's three dot menu, then press "Add to Home screen."