It's not untrue, but it's worth remembering that programming computers in assembly language was quite popular at that time, especially for systems software. Assembly has idioms that can be many lines long, and you tend to recognize them after you've programmed a system for long enough. 10 pages of uncommented, but idiomatic assembly code are more or less the equivalent of 2-3 pages of uncommented (but often idiomatic) C code, which can be fairly manageable.
The code appears to be some of the most ancient Unix Kernel Source Code yet found. This is previous to the PDP-11 1st Edition. Still, many of the familiar bits are there (ed, cat, etc..) A pretty historically significant chunk of code!