Secluded Springs will be headlined by the gen two legendary beasts Raikou, Entei, and Suicune, with the new pack available from 28th August
TAHK0 speculated on why the error may have happened, writing, Poke Balls went through a lot of early variations, with everything from the button placement changing, to how it opens differing, to even being depicted with the white on top. It could be that an early Pok Ball design actually did open like it does on the card back, but when the design was eventually changed to the opposite way, they forgot to update it on the card back before going to print, and it remains that way to this day
These can become highly valuable over time
We've seen prior instances where an alternate art was unpopular, and actually made a card less valuable, but this doesn't seem to be the case here - perhaps there are just more copies with extended art floating around, for whatever reason