This is addressed in the first paragraph of the pdf, with comparisons drawn to other industries and financial instruments where such income is not considered revenue. One can of course disagree whether it should be accounted this way, but the concept is not outlandish.

“This measure, while a standard accounting metric, obscures the strong financial performance of financial intermediaries such as health insurance companies, whose revenues are mostly pass-through payments between insured individuals and their health service providers. […]”

It seems to me that this document is almost entirely an argument for changing the accounting rules because of this distortion.