Now, social media apps are worthless without the aforementioned features that would have to be omitted to get it done in a weekend, so obviously there's some hyperbole going on with statements like that. However, on a fundamental level its correct. The technical requirements of building a social media app are small/easy and within the scope of what a startup on a shoestring budget could manage if they felt like it was a good business opportunity.
The issues start to pile up only much later down the road. Maintaining scalability after you cross some critical threshold of traffic gets hard, but you don't have to think about that until you're at or near the threshold anyway. Not a lot of barrier in getting started.
