Nothing has been leaked yet. Only an unverified report from a new user with another new user supposedly confirming it. These people could have bug bounties in the thousands of dollars, receiving free MacBook Pros from Apple for their troubles but instead he just created an account on macrumors… yeah.Not using iCloud on Windows does not mean you are safe and Windows users will not be able to see your photos. It's been reported that Windows client sees other people's photos, but that does not automatically mean that you need to be on Windows for your photos to be leaked.
Also the “Apple immediately said it is not an issue” is complete BS, having worked with their engineering before