1910 Canadian Quarter Reverse Proof?

The reverse image does not suggest a proof in any way. Better pics needed.

"Reverse proof" dies are actually rather hard to make deliberately. Nobody had the tech to do it back in 1910.

First, to understand how to make a "regular" proof, with frosted devices and mirrored fields. First the design is imparted onto the die by the master hub. Then, the entire die is etched (by acid, or by sandblasting, or these days by computer-guided laser), so the entire die would impart a "frosty" finish if it were used at this stage. Then the top of the die (the parts that create the fields) is polished to death, making those high points of the die (and the corresponding low points of the resultant coins) mirror-shiny.

Making a "reverse proof" is trickier, because you need to find some way of highly polishing just the low parts of the die, while avoiding polishing the high points. Some mints do this by highly polishing the entire die, then putting little stickers down over the devices they want to protect. Then the entire die is etched as normal, but only the bits protected by the stickers don't get sandblasted. You then have to pull the stickers off the die without damaging the surfaces. Mints that use the computer-guided laser to do the etching, simply tell the computer which bits they don't want to etch.

On seeing the "reverse proof" effect on an older coin, where genuinely "reverse proof" dies would be impossible, I would tend to assume improper storage was the ultimate cause; the "frosting" in the fields being some form of oxidation or mild environmental damage, rather than a result of something happening to the coin in the Mint.