The poster was stating that writing Twitter was easy, anyone can do it, the only thing Twitter really has going for it are the network effects of having a huge user base and lots of visibility.
I do think that Twitter's biggest asset are the network effects that it currently enjoys, but I don't think that it would be trivial to recreate what they've done in order to create a Twitter competitor. It's not insurmountable, but it's not trivial either.
The original comment was clearly meant to trivialize the engineering. "One guy can do it in a weekend" is hyperbole, it's something you say when you're trying to communicate that anyone can do something in a relatively short amount of time. If there are a bunch of downvotes I would assume they're more for the hyperbole than people actually disagreeing with whether or not one weekend is enough time to write "non-scaling Twitter", which isn't specific enough for anyone to argue about how long it would take to do.
