That friend is a dumbass who clearly was either not listening or ignoring what the health professionals have been saying. It's infuriating that an at risk individual (diabetes in this case) lost their life even though they've been following the rules just because one idiot so blatantly broke the rules.
It's one thing if they were asymptomatic and spread it by accident but they KNEW they were positive for the virus. And, if asymptomatic, you don't get tested for no reason, so clearly they'd been in contact with someone or someplace with a case and still decided to go to the BBQ after feeling concerned enough to get tested and found positive