Não está concatenado e no console não fala nada.

O erro é apenas esse: Ele não está concatenando meu array de User. Se eu trocar o metodo concat por push ele da o seguinte erro: "Argument of type User is not assignable to parameter of type User" listUser.service.ts

import { HttpClient} from '@angular/common/http';
import { Injectable } from '@angular/core';
import * as $ from 'jquery';
import { User } from '../Users/User/User';

const API = 'https://randomuser.me/api';

@Injectable({ providedIn: 'root' })
export class ListUserService {

    users: User[] = [];

    constructor(private http: HttpClient) {}

    GetUser(){
        return this.http
            .get<User>(API);  
    }

    delay(milliseconds: number, count: number) {
        return new Promise<number>(resolve => {
                setTimeout(() => {
                    resolve(count);
                }, milliseconds);
            });
    }

    // async function always returns a Promise
    async ListUsers(){
        // var users: User[] = [];
        for (let i = 0; i < 101; i++) {
            // await is converting Promise<number> into number
            const count:number = await this.delay(50, i);
            this.GetUser().subscribe(user =>{
                console.log(user);
                    this.users.push(user);
            });
        }
    }
    getUsers(){
        return this.users;
    }

user.component.ts

import { Component, OnInit, OnChanges } from '@angular/core';
import { ListUserService } from '../services/listUser.service';
import { User } from '../Users/User/User';


@Component({
  selector: 'app-lista',
  templateUrl: './lista.usuarios.component.html',
  styleUrls: ['./lista.usuarios.component.css']
})
export class ListaUsuariosComponent implements OnInit {

  users: User[] = [];

  constructor(private listUser: ListUserService) { }

  ngOnInit() {
      this.listUser.ListUsers();
  }

  load() {
      //erro aqui!!!
      this.users.concat(this.listUser.getUsers());
      console.log(this.users);
  }
}

user.component.html

<div class="text-center" (click)="load()" >
    <button class="btn btn-primary">Load more</button>
</div>