| They probably were using a pick as a lot of punk/hardcore bassists do. Or they were using their pointer fingernail. For the ultimate high energy strumming you have to watch Pete Townsend, how that guy lines up a pick with his strings is amazing!
I like to utilize strumming when composing, rarely does it work with an ensemble, but I don't play hardcore, it deffinately can give the bottom end a boost to play two or three strings at once, although chord structure and tone is quite lost. | 
