First of all, the link you posted is to a coin that even though it says is proof, is very clearly not a proof coin, but uncirculated. You have a coin with a COA that states it is a proof. Which would have a mirrored background and a frosted design for this 1986 issue. It is reasonable to have two different finesses. I think that France and maybe some other countries have done this both before and since. To further make this matter interesting is that piedforts for this issue also exist.
Library Media Specialist, columnist, collector, and gardener...
1. Addressing solely the difference between your COA and the Krause catalog fineness:
Around the year 2000, Krause Publications changed its servers, and it was not able to bridge its data files into the new system. They basically had to start over again, and this caused many errors to creep into the listings.
If you go back to the 1991 two-volume ANA centennial edition of the Krause catalog, it does list the business strike of the Statue of Liberty 100 franc 1986 (KM 121) as .900 fine silver, and the Proof version (KM 121a ) as .999 fine silver. 100 franc coins for 1985, 1988, and 1989 show their Proofs as .950 fine silver, and this may be the source of the error (assuming that the COA is correct, which it should be).
(100 franc commemmoratives for 1984 and 1987 show a fineness of .999 for their Proof versions.)
2. As to whether you have a Proof--or a business strike with the wrong COA--examine the coin. It should have mirror fields.
Also look to see if it has the word "Piedfort" near the rim. If so, it is not a Proof, but it does have twice the silver content of the business strike!
