My previous reference is for the skunkworks not for multi-user. Since it's a skunkworks project there is no requirement for the OS to have multi-user so basically Ken is free to design the Unix system as simple as he wished. That's why initially Unix is a single user, flat file, etc [1]. It's not only for single user but also only support single task or process initially. This design of original Unix is the antithesis to the Multics (thus the name Unix) and the latter was designed from the start as per requirements as multi-process and multi-user hence the inherent complexity. Ken is still alive today perhaps you should ask him directly about this fact and I've no reason to believe otherwise.

[1] Unix:

https://en.wikipedia.org/wiki/Unix