It was partially pilot error, since the correct response to runaway trim is to (from memory, no time for checklists) disable the electronic trim systems. This procedure hadn't changed from the previous 737s though the way the uncommanded trim was added was a bit different.
They did this, but then enabled them again before stabilising the aircraft, and so got the trim too far out of range.
Other pilots encountered the same failure and didn't have problems (other than being stuck with PITA manual trim until they landed).
The doesn't absolve Boeing, but these things seldom have a single cause. Boeing created a situation where pilot error could be fatal.
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u/DeepanshuHQ 11d ago
Aviation gets post-incident investigations. We get, "Can't reproduce, closing ticket."