The author believes University can decrease average length of stay without changing quality of care. So the author doesn’t treat the two things as equal. The author believes that they are different and changing one does not necessarily change the other.

The author doesn’t confuse sufficient and necessary conditions. The author doesn’t assert that anything is enough to preserve quality of care, nor does he assert that anything is necessary for preserving quality of care.

This possibility shows that the greater average length of stay at University could be due to having a higher proportion of patients with longer-to-treat illnesses. So, University might not be able to bring length of stay down without hurting quality of care.

The author’s position is that University’s average length of stay could be brought down without impacting recovery rates. This doesn’t mean he thinks the length of stay could be brought down to zero without impacting recovery rates.

What patients prefer has no impact on the author’s reasoning. Even if some might prefer longer stays, the author has statistics that appear to suggest that University can bring down its length of stay without affecting quality of care.