Before the first Phantom came out, everyone was flying homebrewed kits. It wasn't particularly difficult to make; you just had to do proper research and you were able to build pretty much anything. The reason DJI was so successful is because they were able to take a bunch of random parts and package it in a consumer-friendly product. No longer did you have to be a geek or serious hobbyist to fly a drone; you can now buy a finished product.
In fact before I bought my drone I was planning on going the homebrew route. You have control over all aspects of your bird, from the flight platform to the GPS modules and whatnot. You could even buy pre-selected kits that included a shell and all that. In the end it just wasn't worth the time investment and I went off-the-shelf.
BTW this is still SOP in the drone racing world - pretty much everything is home made.
But this guy took the entire idea to an extreme by stripping everything down to the bare minimum, which enabled him to make it this tiny. Most of the size and weight of a regular drone is in the battery, which requires a more powerful propulsion system, which requires more power, and so on and so forth. So like whYME said - the battery life is likely horrendous, there's no stabilization system (definitely no gimbal, and most likely no GPS), and so on.