It found a correlation between cardiovascular health and walking a certain amount a week. This does not at all suggest causation. I'm not nitpicking here. The most likely reason for this is that people who have a significantly more healthy life style have better cardiovascular health while also happening to move significantly more. Just getting up and walking 8k steps twice a week and otherwise having unhealthy lifestyle of the control group is possibly going to do nothing for your cardiovascular health. Claiming anything else needs much different evidence than the linked study.
Edit: I'm not saying walking is bad for you. That's just as wrong. I'm saying just walking won't do much for you. Get a more healthy lifestyle. Cardiovascular health will follow and you'll notice that 16k steps or something comparable will look small compared to what your active/healthy lifestyle will do.