Ironically, I went to an acoustic concert just days later and found the exact same to be true. People came in late and would talk and get situated all while the concert was already fully in progress. Then a woman who was clearly tone deaf started singing along to every song in a quiet concert hall. I don't think she could realize that we could all hear here almost as clearly as the performer we came to see.
All of this made me realize how wrapped up we all become in ourselves and don't pay attention to the surroundings we walk into. I am sure I have done the same thing at some point, I am sure we all do- talking on our cell phones, having conversations with our friends, digging through our purses, rattling things in our pockets. It is the same lesson again and again, isn't it? We need to stay present, be aware of things other than ourselves. Maybe that really is the real lesson in life.