Proofs around the World at this time were not made with mirror fields.
Even as late as the 1960's Australia struck proof coins that did not have mirror fields and certainly NOT frosted devices.
I don't think this is correct, as least for USA coins. Most proofs from the 1860's through the 1890's had at least moderate mirrors unless impaired. Frosted devices certainly occurred and grading services have slabbed plenty with Cameo and Deep Cameo designations. These sometimes have very heavy frost along with deep mirrors. Check out this lot sold by Heritage in 2004 (for about $2000):
Barber proofs starting from 1892 are sometimes seen with super black and white contrast, nearly the equal of modern silver proofs. In any case, it is certainly possible the OP's dime is a proof. The denticles seem a bit weak for a proof and there appear to be significant hairlines in the fields. Better photos are a must to be any more definitive.