Without seeing both tax returns side by side, there is no way to know. You may be incorrect in your assumption that everything is the same.
Even if everything really is the same, your refund is the result of an overpayment, usually due to withholding. If you had less money withheld from your pay, then you got more each week and a smaller refund. Your friend might have had more withheld, so they got less each week and then a bigger refund.
