No, they didn't. They figured out a workaround. Since they didn't find the root cause of the problem themselves and apparently didn't take it up with the Chrome or Grammarly development teams, they don't actually know what happened or when it might bite their customers again.
They say it no longer reproduces on current Chrome/Grammarly, so taking it up with them is fruitless. They're not going to investigate crashers from old versions.
:( I would've tried to determine the cause of the crash with that specific file in my off time, provided that I could isolate the code in the Grammarly extension in Chrome.
The main reason –other than curiousity– is to ensure that a future regression (in Chrome/Grammarly) wouldn't lead to it again.