You're being managed and hustled, that's what managing is in flat organizations.

The mistake in the example is that when Coworker (the antagonist) came to You (the protagonist) and presented a problem by saying, "there's no docs for this," the protagonist answered the question in the context of the problem and not the context of the person and the relationship.

The Coworker in this case invents problems not because he wants solutions, but because he wants You to solve them, and to report the result back to Them, and as soon as you tacitly accept that relationship by giving them an answer, you have accepted that you are obligated to satisfy them, and then they can take that to your colleagues and boss and say you aren't satisfying them. This is what people mean when they use the term "leverage."

If you are technical, you solve problems, so if you have an answer, you give it, and you've solved the problem. What a natural manager does is find problems and uses them as leverage to extract value and power from them. They aren't problem solvers, they are managers, it's a totally different kind of mind. Important, but also often predatory and bullying, so take care.

When someone comes to you and says, "can I get a status on this?" If you give it to them, you have set the precedent that you work for them, and they now have leverage and power over you, even though the org chart doesn't say they do. It's a pure tactic. Since you are generally an agreeable person, it doesn't occur to you to treat their question as an act of aggression, and that's what they're counting on, because their entire toolkit is based on exploiting peoples agreeableness for leverage.

The ability to have the sense to respond to "can I get a status on this?" with, "I'm updating my boss with it, and we can loop you in after," is a skill to be practised. Sometimes the person will just escalate their aggression, and repeat the request, and that's when you know you're dealing with an asshole hustler. The best way to deal with them is to talk to your boss and say you're glad to work on the team, but given the reporting structure, you don't make ad hoc commitments across teams because it breaks up team alignment and if you are a team lead, it rewards other people for interrupting your team members and starting fires.

Short version is, "when I work for you, I will work for you, but until then, that request is out of line." The art is in how you finesse that sentiment and while making it clear. Antagonist Coworker will probably make a scene, try to find people who don't like you and complain about how you are "hard to work with," and encircle you to push you out, and really, navigating that bullshit is 80% of most senior roles that deal with cross functional team competition in any mid size org. It's what I don't like about "flat" organizations, where it really means that this kind of politically aggressive type gets an option on everyones time and attention and then gets rewarded for starting fires. When we moralize weak leadership skills, we reward bullies, and then wonder why our orgs have toxic culture problems.

As a consultant who has worked in dozens of organizations, there's always one of these people, and you have to deal with them as the new kid in school dealing with the insecure bully who creates chaos that always seems to put themselves in the center of it. Sometimes it's the only tool they have, so they don't realize they're doing it and it's just their "personality." It's not. It's a tactic they've practised, and to survive in an organization, you need to actively respond to it, imo.