Scientific discovery and folk wisdom are not necessarily opposed to one another. The elders of the Morgan fisherfolk were really exercising sound scientific method by another name. They drew their conclusions based on observation weighed against the "data" they had on hand, which was the collective experience of their people.

Is that mysticism or is it simply good deductive reasoning? Or is all mysticism rooted in the ability to face the truth square on, without the corrupting influence of personal agenda or rationalization?

Mystical insight, like science, must begin without preconception. Most of the great mystics of the Christian era had to go through something of a dismantling process in order to arrive at deeper faith. Rigid, dogmatic thinking is a roadblock to that process.