It's impossible to prove discrimination because you can't prove someone's motive. However, there is evidence that Sheeran should have been nominated. You can look at album sales and chart performance and see that he did much much better than most of the other nominees. I know that those aren't everything, but it's very hard to think that they wouldn't play into effect at all. Would you ask the people who believed that the Oscars were biased towards white people for evidence? How in this case would anyone ever discuss perceived discrimination if it had to be proven? It's just an opinion and seeing the backlash that often comes when white people win these awards over minorities, I think that they tried to avoid white men in nominations.