I'm guessing here.
Three possibilities I can think of.
1. The boat was offered new with either 1 or 2 spreader rigs - the 2 spreader could be a taller 'race' version
2. Previous owner added additional rigging
to strengthen the rig (going from 1 spreader rig to a 2). If this is the case you should be able to see where the original spreaders came from.
3. The previous owner broke the original rig and when he replaced it there happened to be a locally available mast section of the right length, but its moment of inertia value (Ix & Iy) was less than the original - so additional rigging was put on.
Take a look at the chainplates (inside) - do they look original? If so 1 is probably the case. If not 2 or 3 are candidates