The 50% value was from the river harvest, not the hatchery. The %wild at the hatchery was much lower. Not many wild fish strayed into the hatchery.
From the 2014 DEC report., "The percentages of wild fish in the hatchery from 2009-2014 varied by age and year class but were generally low with weighted (by sample size at each age) averages of 1.4%, 2.2% and 14.5% for the 2008-2010 year classes, respectively."
"The low proportions of wild fish in the hatchery were in sharp contrast to the high proportions of wild Chinook salmon found in the Salmon River angler harvest sample, suggesting that wild fish display a low degree of straying into the SRH. Although wild fish are a substantial component of the Salmon River fishery, they do not contribute much to the hatchery broodstock..."