That is impressive if true. Does he also figure out how to read the WAD files himself too for level geometry and textures? I just find it hard to believe he isn't referencing the original source at all...
Well, the title is "Notch programming a Doom-like in Dart." So, it doesn't sound like it's a port of Doom, just a game that's like Doom.
Was watching and the level he loaded was definitely a Doom one. Looked like the WAD was in his assets.
The WAD format was reverse engineered and published some time back in the 90s when the first third party level editors and mods were produced.