Managers arranging work is _not_ why Conway's law is true though. I think it behooves one to look at the actual text of the "law":
> Any organization that designs a system (defined broadly) will produce a design whose structure is a copy of the organization's communication structure.
It doesn't matter WHO defines or does the work (the coders themselves in a team or the manager). It matters how communication is arranged. And communication naturally aligns itself along organizational and team boundaries.
When a group/person/whatever writes an API they are MOSTLY writing a document for other human beings. That is an act of communication. If you meet with someone everyday in a stand-up you're likely to put a less structured API between yourselves than if you meet with someone once a month, or once a year. You're also going to create a finer grained subdivision of the API for them as you're likely working on closely related posts of the problem.
Organization creates communication, and communication creates architecture. Therefore organization creates architecture.
> Plus conway is just a ... neat idea, not a bound fate
It is in fact bound fate. Code is written to communicate with others.
People come together, they decide to solve a problem. They divide up that problem and create functions (an API), objects (an API), modules (an API), and services/microservices (an API). At each later they've written something that communicates with others. The structure of that code reflects the necessary communication to the other parties for their part of the problem. This the code is structured following the lines of communication in the organization.
Organization is how we structure communication (that's it's primary point) and thus organization = architecture + some wiggle room for communication paths defined outside that (say a SAFE feature team).