Has there been any indication in the reporting that Boston's medical staff may have exacerbated Brown's injury? I have not seen anything but I really only read one piece.
I won't get into the 58 game issue, only Brown knows for sure on that.
As far as the injury itself, I would say it's mildly surprising at first glance he is suddenly out for the season and having surgery. This isn't like a fully torn ACL or Achilles that is an automatic season ender immediately no matter what, in all situations.
Long term these injuries can be problematic and lead to arthritis if untreated (SLAC wrist if anyone is super excited to see some pictures...
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4141341/), but sometimes people will try to play through it and deal with it in the offseason.
Not saying surgery isn't reasonable or needed in his case, perhaps he has known about this for awhile and has already tried to play though it. Perhaps the imaging was so convincing it's unstable and they pretty much know resting won't do anything and they feel he needs surgery ASAP.
But I do wonder if the Celtics were a top 3 seed and a strong contender for a title if he would be going with the exact same plan. It's his non shooting hand, would it be unreasonable to rest it another week or two and see how he feels? Depends on some factors we really can only guess about, so hard to say for sure.
Oh well....Nesmith time I suppose.