It's more likely the opposite. I met a lot of people that use "swear words" in the military, but only a rare few of them had above average intelligence.
That's pretty serious selection bias and does not present a representative sample. Given the stratification caused by testing scores, the "average" intelligence is going to progressively go up as the demands of the Corps and MOS series do.
https://campuspress.yale.edu/yrurp/files/2016/05/Giordano-rg5y5r.pdf