Engines are the responsibility of the engine manufacturer, but often cowlings (which is what failed here) are not. These are highly optimised coverings for the engine which have a big effect on airflow efficiencies, and are often designed by the aircraft manufacturer rather than the engine manufacturer (the engine manufacturer often designs the intake, as that has a lot of effect on the engine efficiency itself).
But this is a 737NG, been in service for years, so its probably a maintenance issue or failed part rather than a design defect.
People need to stop highlighting every failure of a Boeing aircraft now, the vast majority of the ones we have seen talked about this year have nothing to do with Boeing or its culture, and instead are pretty normal failures that wouldnt have been talked about prior to the MAX issues. There are thousands of flights a day, sometimes shit does happen a few times a year - the last time this type of failure was featured on a prime time news segment it had nothing to do with Boeings culture, and it doesnt this time either
Just because a part failed does not mean there is an inherent culture or cost cutting issue, in either the construction or maintenance.