"Willingness to accept the penalty" means you accept the possible consequences of your actions and choose to carry on anyway. It doesn't mean you're supposed to literally martyr yourself for the cause by literally walking yourself into jail so they can torture you.
He was arrested for organizing black workers into a union. That was illegal and resulted in his trial and conviction. The consequence was part of the activism.
Lots of other examples. Freedom riders were killed for defying Jim Crow. While they didn’t wake up with a desire to be murdered, that was a consideration and their martyrdom was part of the movement.
"He was arrested" is not the same as him literally giving himself up and walking himself into jail to be punished for his actions. I have no doubt he knew it was a risk but they still had to actively oppress him for the consequences to materialize. If he became some kind of martyr, it's because they oppressed him for doing what everyone else knew was just.
