My reading of it is they didn't bother to take the motivation of the law into account (suppression of speech), and only took the law "as written" to decide.
> We need not decide whether that exclusion is content based. The question be- fore the Court is whether the Act violates the First Amend- ment as applied to petitioners. To answer that question, we look to the provisions of the Act that give rise to the effective TikTok ban that petitioners argue burdens their First Amendment rights...
The quote you posted is about if the exclusion of platforms "whose primary purpose is to allow users to post product reviews, business reviews, or travel information and reviews" means the law is content-based, but the Court is saying that provision is irrelevant because TikTok brought an "as-applied" challenge (and not a facial one) [0] and that provision doesn't change how it applies to them. So they are looking at the parts of the law (and the congressional record supporting them) which actually cause TikTok to be subject to the qualified divestiture.
they talk more about the motivations of the law in part D.
The "exclusion" referred to in this quote is not the exclusion of tiktok. The court is responding to one of the arguments that tiktok made. Certain types of websites are excluded from the law, and (tiktok says) if you have to look at what kind of website it is, then obviously you're discriminating based on content.
the court is saying that this would be an argument that this law is unconstitutional, period. That's a very hard thing to prove because you need to show that the law is bad in all contexts, and to whoever it applies to, very hard. So tiktok is not trying to prove that, that's not how they challenged the law - instead tiktok is trying to prove something much more limited, ie that the law is bad when applied to tiktok. It's an "as-applied" challenge. In which case, the argument about looking at other websites is irrelevant, we already know we're looking at tiktok. As the opinion says "the exclusion is not within the scope of [Tiktok's] as-applied challenge"