I was also confused because it says on the site about registering your EA first, but you need the product/serial number first

Product SKU: PC Download
Product Name: FINAL FANTASY XIV: A Realm Reborn Pre-Order Bonus Package
Qty Ordered: 1
Amount: $0.00
Serial Number/Product Code: xxxxxx-xxx-xxxxxx-xxx

see if he has this in his email then go to preorder.na.finalfantasyxiv.com and enter that, the email could be from webhelp v4, or Square themselves.