Using System.out.println(Thread.currentThread().getName() + " " +count); leads to synchronization

I was learning multithreading in java, In the tutorial, it said removing synchronized should make the program buggy and it did, So I was just experimenting around and wrote a print line System.out.println(Thread.currentThread().getName() + " " +count); and removed the synchronized word, and even then the program worked fine. But if only synchronized word is removed and the printline(System.out.println(Thread.currentThread().getName() + " " +count);) is not added the program is buggy ad expected.

I can't understand how adding a print line can make it synchronized.

public class intro implements Runnable {

    int n=10000; 
    private int count = 0; 

    public int getCount() { return count; }

    public synchronized void incrSync() { count++;  }

    public void run () {
        for (int i=0; i<n; i++) {
            incrSync();
            //System.out.println(Thread.currentThread().getName() + "  " +count);       
        } 
        } 


    public static void main(String [] args) {

        intro mtc = new intro();
        Thread t1 = new Thread(mtc);
        Thread t2 = new Thread(mtc);
        t1.start();
        t2.start();
        try {
            t1.join();

            t2.join();

        } catch (InterruptedException ie) {
        System.out.println(ie);
        ie.printStackTrace();
    }
    System.out.println("count = "+ mtc.getCount());
}
}