The article states that the twin was not directly associated to the beads (so no putting them on some old twine), but was from the accompanying bangle (probably

The article states that the twin was not directly associated to the beads (so no putting them on some old twine), but was from the accompanying bangle (probably item "o" in the image), which was dated 1397–1488 and "was subsequently affirmed through the testing of charcoal and caribou bones found at the three sites". This is a typical situation when dating items indirectly from their find context. The standard counter-argument is, of course, that the item was added at some other point in time to its find context. So in this case the counter-argument would be that the beads had been added at least a few decades later, while anything else that had been dated is from 1488 or earlier. (A few decades, to allow for some time for their journey from the Atlantic coast to Alaska.) How likely or unlikely is that?