Don't know if this is accurate, but from looking at Mauser stocks on various contract '98 rifles, it might be. IIRC, the idea posted was that the Germanmilitary considered figured walnut as a defect that potentially weakened the stock which made it more likely to break in rough use (combat). The K98s I've had were either plain grain, straight walnut or laminated while a number of South American contract rifles from DWM, Mauser Oberndorf and CZ that I have seen and/or owned had a good bit of fiddleback grain - one was a 1909 Argentine
Infantry rifle that had tight fiddleback running the full length of the stock, on both sides of the stock....and was broken in two at the wrist. Whoever first posited this idea suggested that the figured stocks were culls, and went onto other countries rifles. I agree that no military would intentionally select bad wood for a stock, but final say so on exports would depend on both contract specifications and the customer's inspectors.
BTW, historically, the Scandinavians were very much accuracy conscious and I doubt they'd accept any stock which wasn't strong and stable. Not a lot of walnut grows in the far north, so if they used native woods, it would most likely be beech.
All the best - Dave