He calculated fine, assuming that this is a three-phase installation. That would allow one neutral for up to three circuits. Thus for 8 ccts. : 3 ungrounded conductors
1 neutral
3 more ungrounded conductors
1 more neutral
2 final ungrounded conductors
1 final neutral
1 bonding conductor
---------------------
12 total conductors in conduit

The math seems good to me.

Shawn.