It seems like the torchbearer has some weird attack time changes between ice mode and fire mode presently. namely, attack time is listed as lower in ice mode than in fire mode, and the health damage indicator from normal shots is typically higher when in ice mode against creeps than in fire mode.
That said, it also appears that the Fire Aura skill stacks on the Torchbearer himself, not just on allies as the description says.
Ice Mode Image
Fire Mode Image (start of fire mode; note higher attack time than ice mode)
Fire Mode Image 2 (fire mode after spending time has passed; fire aura appears to have reduced the attack time, and it shifts in increments).