As T stated, the confidentiality requirements apply to the appraiser, not the client.
The appraiser independence requirements in DF specifically allow asking an appraiser to consider additional sales data
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Try to put yourself in the lender's shoes. The AMC/lender have two reports that are using two very different sets of comparables, and they are just trying to reconcile that. Wouldn't the best way to do that be to ask the appraisers themselves about the comp selection? Would you rather they make their own decision about which comps are best without input from the local appraisers (you) doing the work? I would wager that the other appraiser was also asked about the comps you selected.
In short, there is nothing wrong or inappropriate about the request. How you respond is a business decision. You can ignore the request or you can address it and explain why you chose the comps you chose rather than those you were asked to comment on. The choice is yours, and both choices have their own possible consequences.