The primary teeth are very important. They hold space in the mouth for the permanent teeth. If you let a cavity go it could very easily abscess and then you are talking pain, infection, and more invasive treatment.
And your teeth are reflective of your overall health. Teaching your child now to take proper care of his primary teeth and addressing the needs of his primary teeth will set the precedent for healthy permanent teeth.
Because you've never had a cavity it's strange to me that is the reason you question whether you should take this seriously. You were fortunate. But you are being told that your little one has dental needs that need to be addressed so follow up on the screening and have your son checked out.
Seek out a pediatric dentist. They spend an extra 2 years beyond dental school to specialize in the treatment of children and their special dental needs. This includes making it a comfortable experience for the little ones.