Bottom line is it's true they didn't think he was the best QB in the draft (which is why they tried desperately to land other QBs before finally taking him). Like everyone else they appear to have been wrong about that.
But that doesn't mean they lucked into him. They scouted him thoroughly. More thoroughly than any team in the league. And they took him, before anyone else, in the range he was expected to go. That's out maneuvering your rivals for a valuable asset. Even if, like your rivals, you didn't understand at the time precisely how valuable an asset.