This is not a 457b pension, that would be a Deferred Compensation plan
A Non-qualified Deferred Compensation is generally taken into account as wages for FICA (SS and Medicare) purposes at the time when the services giving rise to the compensation are performed, at which time employers are required to withhold and remit the FICA taxes which has happened in your case.
So everything was set up properly for you to receive your compensation over a period of time with only the income tax due. When you receive you W-2 there should not be any withholding indicated in box 4 and 6.
