Read that sentence carefully.
They're counting cat-caused as anthropogenic i.e. part of anthropos-caused aka human-caused. And "single largest group" could be 1% if there are a lot of groups and each happens to be smaller than 1%.
They're counting cat-caused as anthropogenic i.e. part of anthropos-caused aka human-caused. And "single largest group" could be 1% if there are a lot of groups and each happens to be smaller than 1%.