The link is on the right next to the google scholar search results.
If that's correct, I get at that 4% this way: according to https://www.cancer.org/content/dam/cancer-org/research/cance..., about 20% of all deaths are caused by cancer.
If, of that 20%, 0.8% is caused by alcohol-induced cancer, 4% of all deaths caused by cancer are caused by alcohol-induced cancer.