Whenever someone gets an Android phone, it will ask them to log in using their Google account. Unless he specifically chooses not to have it sync, it will sync his contacts. Since Sundar had already copied his contacts over using a microSD card, he has duplicates. Leo would stop syncing using the microSD card, and only sync with Google. Leo lets Google handle all of his contacts and calendar information, and he doesn't keep it anywhere else. The advantage to this is, when he gets a new phone, he just has to sync it to Google and he'll have the same address book everywhere.
Now that he has the duplicates, he'll need to find a way to get rid of them. Leo suggests going to contacts.google.com and merging contacts. He can clean up his address book there, then export it so he has a backup. The he should use the Google address book from then on.