Here is the code section that triggers the treatment of second floor walkways as corridors:
SECTION 1019
EGRESS BALCONIES
1019.1 General. Balconies used for egress purposes shall conform
to the same requirements as corridors for width, headroom,
dead ends and projections.
1019.2 Wall separation. Exterior egress balconies shall be
separated from the interior of the building by walls and opening
protectives as required for corridors.
Exception: Separation is not required where the exterior
egress balcony is served by at least two stairs and a dead-end
travel condition does not require travel past an unprotected
opening to reach a stair.
It looks like the 10 feet requirement comes from the accessible means of egress section:
1007.7 Exterior area for assisted rescue. The exterior area for
assisted rescue must be open to the outside air and meet the
requirements of Section 1007.6.1. Separation walls shall comply
with the requirements of Section 705 for exterior walls.
Where walls or openings are between the area for assisted rescue
and the interior of the building, the building exterior walls
within 10 feet (3048 mm) horizontally of a n,onrated wall or
unprotected opening shall have afire-resistance rating of not
less than ,1 hour. Openings within such exterior walls shall be
protected by opening protectives having a fire protection rating
of not less than 3/4 hour. This construction shall extend vertically
from the ground to a point 10 feet (3048 mm) above the
floor level of the area for assisted rescue or to the roof line,
whichever is lower.