Link Bubble uses the Android WebView for rendering, yes. But the API is pretty deficient in a few key areas, and I will likely have to switch to a custom modified version of Android 4.4's WebView at some point.
If the app uses Android WebView for rendering, then its description on the Play Store as an "all-new browser" is a little disingenuous. The article by The Next Web[1] that is quoted in the description on the Play Store starts off by comparing the app with Chrome, Firefox, Dolphin and Opera, which seems to reinforce the wrong impression.
[1] http://thenextweb.com/apps/2014/03/21/link-bubble-reimagines...