“...the ship took its final voyage around 280 B.C., at least a decade later than previous dating had indicated.”
Sounds like they merely substituted one wild-assed-guess with another.
Well, if the coin is accurately dated to 294 B.C., and many ancient coins can be dated to a year or to a narrow range of years, the ship wreck would have to be later than 294. So at least they are in the ballpark.