It was both, but they bootlooped for different reasons. Nexus 5 had a faulty power button that could fail in a couple of ways. Nexus 5X was something about how the components on the PCB were constructed being of iffy quality. You could get lucky and never have the 5 fail whereas the 5X was/is guaranteed to fail. I bought a 5X purely for device testing. It was basically unused 99% of its lifetime (6+ years) and eventually started bootlooping last year.