Typescript implicit casting to interface not working [duplicate]

I have a .net core web api that returns a list of ethnicities with a number of properties. Using the angular httpclient I call the api and return the data. When I subscribe in angular and cast the data to a much more simple interface, the full object is mapped / cast. Not what I was expecting.

Here is what I have:

export interface IEthnicity {
    id: any;
    ethnicity: string;
}

export class AppComponent {
  ethnicities: IEthnicity[] = [];

  constructor(private svc: MyServiceService) {
    this.svc.getList().subscribe(
      resp =>{
        this.ethnicities = resp as IEthnicity[];
        console.log(this.ethnicities);
      }
    );
  }
}

I was expecting my ethnicities array to hold a list of the same type as the interface but it is an array with the same type as returned by the web api.

e.g.

0: {Id: 'abc1', OrganisationId: 'org1', Ethnicity: 'Indian', IsDeleted: false }
1: {Id: 'abc2', OrganisationId: 'org1', Ethnicity: 'White', IsDeleted: false }
2:
   Ethnicity: "Chinese"
   Id: "abc3"
   IsDeleted: false
   OrganisationId: "org2"
3: {Id: 'abc4', OrganisationId: 'org3', Ethnicity: 'Irish', IsDeleted: false }
4: {Id: 'abc5', OrganisationId: 'org2', Ethnicity: 'Arab', IsDeleted: false }

Notice the properties do not match the interface, The capitalisation of the first letter of the name of the property and the double quotes " instead of single quotes ' around the expanded array item values.

Regardless of what is actually coming back from the api, the resp as IEthnicity[] should cast the values to the two interface properties only. What am I missing?

Update

For anyone who has the same problem, a simple answer is to use the map function in rxjs. Don't forget to include the following import import { map } from 'rxjs';

    svc.getList().pipe(
      map((list: any) => list.map((ethnicity: any) => ({ id: ethnicity.Id, ethnicity: ethnicity.Ethnicity }) as IEthnicityType ))
    )
    .subscribe(
      data => {
        this.ethnicities = data as IEthnicityType[];
      }
    );

Hope this helps