I would say that that is just a contributor in the rapid increase of bitcoin's value and it is not the reason. The reason is the demand of bitcoin is quickly rising, thus making bitcoin's value to increase. Though Japan's move is a major trigger, still, for me, it is just a contributor (and by just a contributor, I mean a major contributor) for the soaring high of bitcoin value.
Being a contributor that could affect the volume and demand to increase rapidly does mean that it is not a mere contributor for the price rise ,their decision has made some ripple in the price of bitcoin and that is the reason we are seeing the price of bitcoin breaking many records.