Contributions returned normally refers to a refund of contributions you made to a retirement account and withdrew before the due date of your tax return. You are allowed to do this if you change your mind and want your money back or you simply contributed too much to your retirement account.
Employee contributions refers to the amount you contributed from "after tax dollars" to your retirement. When you receive a distribution, part of it is not taxable, since a portion of your pension contributions are from income that was already taxed.