Java 8 method reference does not start thread?

Why does a method reference not start a thread in this example?

package example;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class ESMethodReference {
    int i1, i2, result = 0;

    ESMethodReference(int i1, int i2){
        this.i1 =i1;
        this.i2 = i2;
    }

    public Runnable calculate(){
        System.out.print("In calculate()");
        return new Runnable() {
            @Override
            public void run() {
                result += i1 + i2;          
                System.out.print(" creating result");
            }
        };
    }

    public static void main(String[] args) throws InterruptedException{
        ESMethodReference es = new ESMethodReference(1, 1);

        ExecutorService executorService = Executors.newSingleThreadExecutor();

        for (int i = 0; i < 2; i++){
            executorService.submit(es.calculate());
            Thread.sleep(100);  // Allow new thread to run      
            System.out.println("\tes.calculate() result incremented " + es.result );

            executorService.submit(es::calculate);
            Thread.sleep(100);  // Allow new thread to run      
            System.out.println("\tes::calculate result NOT incremented " + es.result );
        }

        executorService.shutdown();
    }
}

Output:
In calculate() creating result es.calculate() result incremented 2
In calculate() es::calculate result NOT incremented 2
In calculate() creating result es.calculate() result incremented 4
In calculate() es::calculate result NOT incremented 4