I think it highlights a distinction between Apple's past work and their recent work.

Google forked Blink because for whatever reason they were unsatisfied with the state of Webkit -- nominally because they wanted to take a different approach to multi-process, but there may have been other technological and project direction/pace disagreements. Since then, a number of browsers have switched from Webkit to Blink/Chromium as their engine, and arguably Safari is falling behind on new features and overall quality (weird quirks that require web devs to work around).