Why ngDoCheck is called when setTimeout is resolved?

I'm trying to understand why ngDoCheck runs when setTimeout is resolved.

I've a simple component like this.

@Component({
  selector: 'app-child',
  templateUrl: './child.component.html',
  styleUrls: ['./child.component.css'],
})
export class ChildComponent implements DoCheck {
  constructor(private cd: ChangeDetectorRef) {
 
    setTimeout(() => {
      console.log('setTimeout done');
      // DoCheck runs
    }, 5000);
  }
  ngDoCheck(): void {
    console.log('Child DoCheck: ');
  }
}

after 5 secs, I get logs like:

setTimeout done
Child DoCheck: 

Why ngDoCheck was called? even though no state/model/binding was updated

I get the general concept when ngDoCheck is called:

• whenever angular change detection runs
• to capture changes that angular otherwise doesn't.

Is there some sort of binding of promises, setTimeout with zone js that calls ngDoCheck whenever the call is resolved?

If so, I want to see zonejs code or any actual source from docs that confirms it.

Also, what is the purpose of calling ngDoCheck when simply console logging a setTimeout? I mean this use case application.

As mentioned in angular documentation:

> Zone.js is a signaling mechanism that Angular uses to detect when an
> application state might have changed. It captures asynchronous
> operations like setTimeout, network requests, and event listeners.
> Angular schedules change detection based on signals from Zone.js

Here is the code from angular repo how it monkey patches setTimeout

Zone.__load_patch('timers', (global: any) => {
  const set = 'set';
  const clear = 'clear';
  patchTimer(global, set, clear, 'Timeout');
  patchTimer(global, set, clear, 'Interval');
  patchTimer(global, set, clear, 'Immediate');
});

Source code for patchTime