Of course he was a traitor by British law! Stupid question.
The American colonies launched a revolution, which is by definition a revolt against an existing political and legal system, using (again by definition) illegal or at least non-legal means.
Revolutionists are heroes if they win, and traitors if they lose.
Treason doth never prosper: what's the reason? Why if it prosper, none dare call it treason.
“Revolutionists are heroes if they win, and traitors if they lose.”
The south never had any chance of winning. They made a stupid choice to rebel.