You're right that at 50 yards half-inch groups are not uncommon, especially with 54 action rifles, and even more so with 54 action rifles with match chambers. But as with so many things there are qualifications that should be considered, even when shooting conditions are ideal and identical.
Not all barrels are equal, even within a given model. That is to say some barrels will be better or worse than others, while the majority of them will be average for that manufacturer.
Not all ammo is equal, between different brands and even within a given variety of a certain brand. Good quality ammo is made in different lots, some of which will be able to produce better results than others in the same barrel.
Shooting is a skill that can improve or deteriorate. A rookie with the best rifle and ammo is not likely to shoot an Anschutz as a concert pianist plays a Steinway. Very few shooters have the experience of shooting their best results with a rifle the first few times they try it out. Quite often results can be improved upon as the shooter becomes more familiar with the rifle.
I don't know if any out-of-the-box unmodified Anschutz has the potential to consistently shoot half-inch groups out to 100 yards. That would be a very demanding challenge indeed. The greater the range, the more necessary it is that the ammo be the best possible. Perhaps a very skilful and experienced shooter with very good ammo might be able to do it, but no doubt a little luck would also be needed.