That appears to be the slip cover of the release with the ... with a signed letter from John Carver himself. Thanksgiving already had a standard Blu-ray release earlier this year.

Thanksgiving is available on Ultra HD Blu-ray with a Dolby Atmos or a 7.1 Dolby TrueHD audio presentation if Atmos is not supported. This review will cover the Blu-ray’s Dolby Atmos mix.

As of Nov 25th, you can only watch A Charlie Brown Thanksgiving if you sign up for a free 7-day trial with Apple. It still makes it "free" to watch, but via a proper sign-up from here on out.