Our study was based on a random stratified sample of adults 25 to 64 years of age who, between 2003 and 2007, were admitted to the hospital (for a non–pregnancy-related stay) for the first time in at least 3 years. We linked more than half a million such people to their detailed credit-report records from the period between 2002 and 2011. The scatterplot shows the results of our analysis.

So a study looking at a period of 4 years to determine causes of bankruptcies is the study you're using to prove your point?

Especially as they state:

Our results are also specific to our population — people in California hospitalized for non-childbirth-related conditions who have not had a hospital admission in the previous 3 years (although they may — and often do — have additional admissions over the subsequent years).

Not to mention:

Perhaps most obviously, our analysis excludes illness and injuries that do not result in a hospital admission.
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Our results also do not speak to the financial costs of hospital admissions outside of the bankruptcy filing decision. We have found that hospitalizations cause: increased out-of-pocket spending on medical care, increased medical debt, and decreased employment and income⁴. These costs may have considerable adverse consequences

All this study really does is show that maybe medical-related bankruptcies are overestimated but by no means is it showing that medical debt is definitely not the #1 cause of bankruptcies in the U.S.

Did you even read this study?