I learned to swim in the early ‘60s at the Multnomah Athletic Club in Portland. Everyone wore swimsuits. Later, from 1968 to 1972, I went to THSFKAW (The High School Formerly Known as Wilson), which had a pool. Everyone wore swimsuits.
I never heard about boys’ nude swimming at any school in the Portland area when I was growing up.
According to the many posts here it was a ‘thing’, just not in your area...............