Yes,Thanks for pointing that out. Chromium doesn't have to be licensed and can be installed additionally like firefox.
For embedded solutions updating the software often is not easy. The devices in general are not "personalized" and don't come with some app store installed.
A separate Chromium install means more work but also offers the chance to update the Browser more often.
An Android integrated and maintained browser makes it easier/saves some work for the OEM as he doesn't have to care for a separate browser.
they write "... The WebView shipped with Android 4.4 (KitKat) is based on the same code as Chrome for Android version 30. The WebView does not have full feature parity with Chrome for Android and is currently given the version number 18.104.22.168.
Your apps inside a WebView are just as important and deserve a runtime that keeps users up to date. There are large engineering and logistical challenges. We're not quite there yet, but we're working on it."
I'd interpret "logistical challenges" as a reference to the play store.
At the moment I don't see if a later installed chrome or chromium app can/will affect the webview.
If the webview isn't "updated" by a separately installed chrome/chromium app a webview based browser would offer advantages in terms of consistency (same rendering in browser and webview).