Granddad had sex with one of my guy friends

My mom and I don't talk. I was raised by my grandparents. My mom told me her dad molested her and her brother and he's a P3DO. My grandparents always said my mom was crazy and bipolar. Now I'm finding this out and I need opinions because it's not exactly like what my mom said happened to her and my uncle but I feel weird about it. I rekindled a friendship with one of my guy friends. He's been sober 2 years. He was addicted to pills. He told me that he had sex with my grandfather when he was 19. He said he was going through withdrawal and my grandfather offered him some narcs. He didn't have money so he traded it for sex. My friend is straight but he said he was so low and withdrawal symptoms were awful. He wanted it to stop. So he agreed to have sex with my grandfather who would have been 67 at the time. He described what happened and it made me kind of sick. He did consent. But he said my grandfather ripped his underwear off and was pushing his head into the bed and he knew he didn't want to but needed the drugs. He told me he cried the entire time it was happening. He knows he consented but the whole time he felt like he was being raped. He felt violated. He's glad to be sober now. He was a legal adult and he did consent. Thing is it's still so weird and creepy. In your opinions could what my mom said have been true?