Social Media Addiction has become a popular belief that is misunderstood. Which is understandable, considering that public knowledge of child psychological development and developmental psychopathology is minimal.
Technically, an addiction is a repeated behavior that is used to seek relief from anxiety. For which nature has created an innate psychological mechanism: the obsessive-compulsive ego defense which is very effective. An obsession is a recurring thought and a compulsion is its associated recurring behavior. Thus a person might continually worry whether they locked the door and repeatedly check if they did with this behavior relieving their anxiety though it has nothing to do with the door. Similarly, a youth may become obsessed with social media not from its content but because it meets their need to reduce anxiety stemming from family or social or school issues.
A source of confusion is that the DSM (Diagnostic and Statistical Manual of Mental Disorders) is poor for understanding, being based on symptoms rather than psychodynamic understanding. The theoretical term, Elements of a Borderline Psychotic Psychostructural Organization, underlies many if not most child and adult mental health symptoms. What it indicates is not psychosis or borderline psychosis but weakness of one or more, in varying degree, of the basic ego capacities governing thinking and behavior, affect modulation, and having a sturdy sense of who one is (one's "sense of self").
Developing during early childhood from the lack of a "good enough" (not perfect!) parenting, it can cause a wide range of symptoms that interfere with a teenager's ability to achieve the critical developmental tasks of separating appropriately from parents, making provisional educational and vocational decisions, developing a secure sense of who they are, and dating, leading to painful anxiety and the possible search for relief through obsessive-compulsive activity using a phone or tablet, this not however causing it.
So Virginia, when you hear the words, social media addiction, smile politely but don't say anything. Knowing that, about this, you're smarter than many grownups.