It's a relatively common thing that Amazon has Schleich products listed months before they are officially released. Not only the regular stuff but also exclusive figures and sets. On our German Amazon I frequently come across those sets though the exclusive horses are never listed before their release here.
And it's also common that you can find one set (or figure) but not find the rest. I see myself already searching for the new Schleich from 2024 in October and getting mad because of finding one figure in Horse Club and the others still don't show up...
Well at least it's a good sign that this model definitely exists and will come out in September like he should.
Now I am looking forward to see the Morgan mare.
So yeah, I'm sure that the listing is real.