“Others who had assembled in the caves nearby in order to observe the seventh day secretly were betrayed to Philip. They were all burned together, because their piety kept them from defending themselves, in view of their regard for that most holy day.”
This is a reference to an incident that is somewhat the same in 1 Maccabees, chapter 2 about people who would not fight on the Sabbath. There was no indication of Phillip in 1 Maccabees, but the idea is the same, the refusal to fight on the Sabbath. Here they were burned for merely observing the Sabbath, while in the other story they were hiding in the wilderness. Thus we have Jewish martyrs for the cause of the Sabbath.