How does Stowe say the man’s lack of education helped in this situation?

This would mean that Symmes is ignorant of the law that forbids him from assisting Eliza in her flight. Symmes acts in a Christian manner, and helps her, as opposed to stopping her and turning her in. Stowe is making a statement, this is HER story. Thus, she is alluding to the fact that Symmes actions would have been different had he known about or understood the Compromise of 1850.