I wonder if this has any relation to the other "lane wondering thread" maybe that is their problem. Did you notice anything like that before the fix?
If you were to look at the wheel assembly, the "line" that runs from the top center of the strut through the hub center is the amount of caster, or steering axis inclination, SAI, from a perpendicular line from the top center of the strut to the ground. You can also visualize it using string if it helps, just run a string line from the top center of the strut to the ground, then run another line from the same top point through the center of the hub.
The degree of the angle at the top of the triangle is the caster angle.
Regardless of the toe and camber settings, if one wheel has an angle more than .5 degrees positive over the opposite wheel, it will allow the car to drift, or pull, toward that wheel.
So with the right front wheel more positive toward the perpendicular, it would drift/pull to the right. By correcting the SAI of the wheels to a more equal caster angle, or anything less than a total angle of .5 degrees, it corrects the drift/pull and makes steering more stable.
A half inch, in terms that was measured, is a lot of caster difference, so yes, this could be the cause of the drifting.