Essentially any contact with a hospital in that population produces eye-popping statistics. Having worked in this area, I’m of the opinion that the presentation of this work is misleading.
It's all confounded. If you compare to other hospital admits, you're finding an even-less-healthy population (because they had a reason to show up to the hospital -without- COVID). If you compare to the general populace, you risk inadequately controlling the comparison.
But if you want to know the increased risk people have subsequent to COVID hospitalization, perhaps the latter makes the most sense to measure.
[1]: https://en.m.wikipedia.org/wiki/Strengthening_the_reporting_...