Komentarz do Diwrej ha-jamim II 21:9

who surrounded him He smote those Edomites who surrounded him and supported him to aid him, for it was their custom that when they were victorious in war, they would seize the mighty men and bring them with them lest they join their enemies to aid the Edomites, their countrymen. In this case, he got up at night suddenly and slew them. Our Sages, however, explained “those who surrounded him” as “those near him.”