I find it so heartwarming that bg said he felt emotionally moved by the fans singing along to sb’s cover, even though he wasn’t the one performing. It’s almost like he’s saying to sb, “your joy is my joy, and your fulfillment is mine too.” He was genuinely happy that the fans appreciated sb’s singing, knowing that it would bring sb a sense of accomplishment. It also subtly acknowledges how powerful sb’s performance was, touching the audience enough for them to want to sing along, which is a testament to how impactful sb’s singing is.