Ethical vegans tend to describe people who are simplying choose a diet without animal products as plant based eaters. So that would not necessarily be Vegan as they could be exploitative in all other manner than food. Of the people who don’t want to associate with veganism, they often also refer to their diet as plant-based rather than Vegan.
So while we can’t know for sure if SFB is an ethical Vegan, the fact that he’d self-described as Vegan rather than as a plant-based eater is a very good indication of his beliefs. I am not aware of any text describing the particulars of his belief, but I think it’s best to assume in good faith since he uses that exact word.