You are not bound by the NDA. However, you are likely bound by something that the NDA addresses. Likely what's going is something along these lines:
When you were hired, you were told that you are not to reveal confidential information without authorization.
Your employer signed an agreement with another entity, and that entity agreed to not reveal anything.
Your employer is now satisfied that this other entity won't reveal what it's told, and therefore has authorized you to tell them confidential information.
So you're still prohibited from revealing information without authorization, but you've received authorization, and you've received that authorization because the entity signed the NDA.
Your employer has also agreed to not reveal information it receives from the other entity. So now any information the entity gives you falls under the category of "confidential information", and is covered by your original agreement with your employer to not reveal such information.
The NDA your employer signed with the other entity does not directly apply to you, but it does prohibit your employer from revealing information, and obligates your employer to instruct their employees to not reveal information. Since you've agreed to follow your employer's instructions regarding confidential information, their instruction is binding on you, and since the instruction is due to the NDA, the NDA indirectly applies to you, through your original employment agreement.