The study explicitly states, that the problem went away for reddit, but this does not proof that the hate went away, it maybe just left reddit for another platform.
Sure but I interpreted the claim being made to be about hate existing anywhere. Reddit can do what they want, but we can argue whether it's good for society or not, even if it's clearly good for reddit.
There's a difference between policing your own corner of the internet; versus policing the entire internet.