Good eye, Gus!
Yes, it is a 3-phase panel. The arrangement of the neutral buss leads me to suspect that this is a dayed panel; it looks like a "Myers" panel I encountered on another job, which would use Cutler-Hammer breakers as replacements.
This was probably installed long before there even were ground wires. I would suspect that the wall is masonry, and the back of the panel simply rusted apart. The wood is a repair.
