I can't speak for anyone else but this is just after going through it several times today. Two observation. (1) flexible alliances of the moment has been recorded as happening, ummm, since they've been recording history in the Middle East. (2) ISIS drew much of its membership from AQI [Al Quadai in Iraq] and I'd put far more weight on this rather than ISIS being too violent for Al Quadai can accept. As such, they likely received some members with the appropriate skillz.
Not that any of this matters to various media, corporate and political cyber-hype machines. As for me, I'm disconnecting my valuable machines away from any connectivity, not just the web. Friendly-fire, for some damned reason is usually, distressingly, more accurate than enemy-fire. Just saying (veteran obs.)