This is new one to me too, weirdly clean. Despite what a couple others have said, nails were a very common drywall fastener in the era of dimensional lumber joists and cross braces. Lack of strapping has absolutely nothing to do with it. Properly nailed drywall is plenty strong. Either this was not properly nailed and/or there is an underlying structural issue.
Although the whole building was quite likely handled by one drywall contractor, often there is multiple subcontracters installing. Other units could be fine. I would inspect any unit you are offered or consider calling the city for a safety inspection.
Drywall just shouldn’t do this. If you do not have tenants insurance already, get some now. It is cheap.