Pierre
The bonding might have been a "field decision" by a coworker but more likely it was in the prints.
When I got to the job there was a wood curb wrapped with rubber roofing membrane, inside the curb was a 12/2 MC and a 4/0 bare waiting to be landed on the fixture.
My guess is this was part of lightning protection, the fixture was lagged to the wood curb material so the fixture would have been isolated from building steel other than the 12 AWG EGC with the MC.
Bob
