That study (full text[1]) is extremely selective: namely, the only factor they looked at was hospitalizations causing bankruptcies, and ignored emergency care expenses, chronic conditions and other long term treatment. In fact from their introduction you can very much see the problem:
the fraction of people filing for bankruptcy who happen to have substantial medical expenses.
Like...that is a weird factor to just try and wash away with sample selection.
The only factor they considered was the proportion of people who filed for bankruptcy by years before/after hospitalization, which they found was about 4% of total bankruptcies - for non-elderly adults.
we estimate that hospitalizations cause only 4% of personal bankruptcies among nonelderly U.S. adults, which is an order of magnitude smaller than the previous estimates described above.
Now let's put that in perspective: one of the most common routine surgeries for a healthy person would be having your appendix out. That's a hospitalization, you stay overnight. It's also fairly cheap and immensely routine.
It is also notable that the study was focused on patients at a single Californian hospital -
we therefore selected a sample of people who were admitted to the hospital in California
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
In short, the way this study is being thrown around to assert how medical bankruptcy works is invalid. And I'm calling completely bullshit on this methodology. Even their conclusions more or less paint the picture:
We have found that hospitalizations cause: *increased out-of-pocket spending on medical care*, *increased medical debt*, and decreased employment and income
* asterisk emphasis mine.
[1] https://pmc.ncbi.nlm.nih.gov/articles/PMC5865642/