It's hardly a surprise twist or anything: Worf already told us exactly how fast Soran's probe would be.
Worf: "Sir, according to my calculations, a solar probe launched from either the Klingon ship or the planet's surface will take eleven seconds to reach the sun."
Note that Worf had no real data on the specific hardware the Klingons or Soran would be using. He had no sensor readings on the launch installation on the surface, and Soran's previous starkiller probe at Amargosa had apparently been of a standard Starfleet model. So we learn that all
"solar probes" span these five to ten lightminutes from a Class M world to its star in eleven seconds - fairly humdrum performance for a warp drive, really (except when close to a star, but perhaps that only applies to larger starships?).
Not much need for speculation here. The probe had a FTL drive, just like so many others, despite starting its journey at a fairly low speed riding on a conventional-looking rocket flame, just like so many others.