I expect the latter. Social media isn't social in any meaningful sense. It is more like an interactive diary or interactive television. Any human involvement behind the scenes is merely an implementation detail — and with the way AI is going, an implementation detail that may not even remain for much longer. Social media may reduce overall social interaction, but only in the same way that reading books reduced social interaction. There is only so much time in the day; but that doesn't make all uses of time equivalent.