The OPSU might have indeed failed or become clogged (the opening is pretty small and it clogs pretty easily. It could also have a loose/dirty harness connection, or the o-ring on the oil tree could have failed.. when it goes you usually just see lower oil pressure through the sensor; the oil pressure isn't actually down, but less oil is being forced through the filter+sensor, which obviously isn't great either.
It could also be the gauge; our clusters kind of suck.