Okay so digging in to this on a site that publicly lists all changes to the Steam registry, I've been able to wiggle out a few extremely thin details by taking the App # from the leaked achievement icon.
For starters, it's been in the Steam registry for about three months. Apparently a (probably non-public) store page went up for it for a few days under the name "Untitled Game (DH_DLC)". That store page was removed 11 days later.
Believe it or not, the game has a Steam Community Hub:
http://steamcommunity.com/app/222920
There's nothing there, though, except for a single screenshot that looks like it was either deleted or is privated. Going to the profile page of the guy who posted the image (ascarlston), Steam lists him as owning one game but nothing publicly shows up in his game library. Friends on his friends list are in similar boats - "joseguera" is listed as owning ten games, but only three display publicly.
Interestingly, "joseguera" is friends with who appears to be a gameplay programmer at Double Helix Games. Maybe that's who's making this Strider thing? The "DH" in the game's temporary store name would definitely suggest Double Helix.