While its primary mode is indeed method-for-sending-pointers-to-media, it also has an option for streaming the contents of a Chrome tab directly to the Chromecast device [1] ala-VNC. With caveats: that feature is still in beta and requires a fast computer/connection.
It is using open standards upnp+rest api+websockets. The mirroring part is done with opus and vp9. Miracast on the other hand is drm(big players only) over drm(restricted content) over drm(it will only work with closed source software). Miracast will only live in heads of Balmer worshipers and maniacs, who love to to create long power point presentations with lots of bullet points.
The DRM in Miracast is pretty much the same as the stuff sent over HDMI. Wouldn't surprise me if the Chromecast requires HDCP like Apple TV does.
Also, if your assertions are correct, please update the Wikipedia page, which states that "At present time, Miracast Source is mainly active on Android platforms." which seems to conflict with "only ... Balmer worshipers".
[1] https://chrome.google.com/webstore/detail/google-cast/boadge...