As Beth pointed it out, the fact that the Queen wore that very brooch on the official 25th anniversary photos could have made the confusion.
In my opinion, just the diamond fleuret earrings were a 25th anniversary gift from her husband:
Here are the clearest photos I have of that beautiful brooch :
The emeralds seem to be gorgeous!
Yes, its strange that neither the Queen nor Camilla wore it...
For the provenance of the brooch, I really don't know but yes, the Greville source is a real possibility.