As far as my understanding goes the law that went into effect in February enabling people to carry in National Parks pertains only to the people that have concealed carry permits. Doesn't matter whether you open carry or not, you still need a permit to carry into the National parks.
Someone correct me if I'm wrong though.
Nope, the park follows state law. You may have the original NPS rule confused with the later congressional amendment. From the NPS
"Congress approved a new law allowing loaded firearms in national parks starting Feb. 22, 2010. That means people can openly carry legal handguns, rifles, shotguns and other firearms and also may carry concealed guns as allowed by state statute."
More info here.