This is the most important part

> Predisposing factors included a remote history of gastric bypass and recent prolonged antibiotic therapy

I knew as soon as I saw it, and the keyword confirms it: a fluoroquinolone, moxifloxacin was used.

FQs like cipro and levaquin are well documented to cause permanent full body damage through all sorts of mechanisms. Including acute kidney injury https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3708027/

And the effects are worse for older populations.

The diet was likely unrelated to the kidney injury.