Kinda both. If you look at the side to side turning in chum kil, are you using your hip or waist to lead the movement. Or if you look at a forward and backwards bending, kulo wing chun has a motion called wan wun yiu, which is an emergency technique involving controlled bending back with the force of the opponent's strike to recoil forwards with a counter.
Just read this. Its interesting, it seems, strangely enough that Ku Lo wing chun has more in common with Guangzhou wing chun than it does with Yip Man wing chun.