Again: every browser on iOS is a Safari reskin because it cannot be otherwise. Safari and WebKit are essentially the same thing (download WebKit on Mac to find out)
Only “remote browsers” like Opera Mini can currently use something other than the system’s webview.
More specifically it uses WKWebView. You can’t compile WebKit yourself to include in an app, which means less flexibility than non-iOS WebKit apps and Chromium forks. Their complaint is valid (“reskinned safari” is just a casual way of saying this)