With any imbalanced posture (postural distortion pattern), including text neck posture, asymmetrical pathomechanical forces are placed into the tissues of the body. These forces have to have an effect. I believe it is impossible to argue that pathomechanics do not lead to dysfunction.
That people aged 18-21 in this study have not yet begun to experience pain as a result of text neck posture does not surprise me at all. They are simply still too young to experience what the physical stress of the overuse of text neck posture will eventually do to them.