AS I read here at RTI India, that the CPIO has the power of revision, so I guess if the information is supplied and signed by PIO, that should be sufficient. Also sicne CPIO is the only public authority who needs to supply the information, it is ok that PIO has signed it.
However, if you are referring to AA decision, then offcourse it should be signed by him.
In you case, if might be that the AA has directed the CPIO to supply the information, and CPIO intrun had supplied the information under his signature. If that is the case the information is valid.
You can ask for the decision of the AA in his signature. The AA cannot supply the information, he can decide the appeal and direct the CPIO to supply the information.