The origin of a Blob URL
must be the same as the origin specified by the incumbent settings object at the time the method that created it was called.

This is stated as a normative statement, implying to me that blob URL's have some special origin that must be set at creation time.

However, the origin of a blob URL is instead normatively determined via the URL Standard. So this is just a statement of fact about what happens to be true according to the below algorithm, which is what creates blob URLs.

So it should be changed to a statement of fact, instead of a "must":

The origin of a Blob URL will be the same as the origin specified by the incumbent settings object at the time the method that created it was called.

Furthermore, this would be much clearer if instead of defining the new term "origin of a Blob URL", it just linked the first "origin" in this sentence to https://url.spec.whatwg.org/#concept-url-origin