"Just interpreting the law"? The article (which you mischaracterize as a blog post) says:

"Thomas’s “two-sided market” claim is an invented rule, conjured specifically to aid American Express in its quest to extract maximum revenues from retailers. “I am not aware of any support for that view in antitrust law,” wrote Justice Stephen Breyer in a scathing dissent he read partially from the bench.

So, where is the law concerning two-sided markets? Here's why Breyer writes in his dissent:

"The majority disputes my characterization of merchant-related and
shopper-related services as “complements.” See ante, at 14, n. 8.
The majority relies on an academic article which devotes one sentence
to the question, saying that “a two-sided market [is] different from
markets for complementary products [e.g., tires and gas], in which
both products are bought by the same buyers, who, in their buying
decisions, can therefore be expected to take into account both
prices.” Filistrucchi, Geradin, Van Damme, & Affeldt, Market
Definition in Two-Sided Mar­kets: Theory and Practice, 10 J.
Competition L. & Econ. 293, 297 (2014) (Filistrucchi). I agree that
two-sided platforms—at least as some academics define them, but see
infra, at 19–20—may be distinct from some types of complements in the
respect the majority mentions (even though the services resemble
complements because they must be used together for either to have
value). But the distinction the majority mentions has nothing to do
with the relevant question. The relevant question is whether
merchant-related and shopper-related services are substitutes, one
for the other, so that customers can respond to a price increase for
one service by switching to the other service.

The "infra" is:

> What about the academic articles the majority cites? The first thing
to note is that the majority defines “two-sided transaction platforms”
much more broadly than the economists do. As the economists who
coined the term explain, if a “two-sided market” meant simply that a
firm connects two different groups of customers via a platform, then
“pretty much any market would be two-sided, since buyers and sellers
need to be brought together for markets to exist and gains from trade
to be realized.” Rochet & Tirole, Two-Sided Markets: A Progress
Report, 37 RAND J. Econ. 645, 646 (2006). The defining feature of a
“two-sided market,” according to these economists, is that “the
platform can affect the volume of transactions by charging more to one
side of the market and reducing the price paid by the other side by an
equal amount.” Id., at 664–665; accord, Filistrucchi 299. That
requirement appears nowhere in the majority’s definition. By
failing to limit its definition to platforms that economists would
recognize as “two sided” in the relevant respect, the majority carves
out a much broader exception to the ordinary antitrust rules than the
academic articles it relies on could possibly support."

Breyer ends:

"For the reasons I have explained, the majority’s decision
in this case is contrary to basic principles of antitrust law,
and it ignores and contradicts the District Court’s detailed
factual findings, which were based on an extensive trial
record."

This is in accord with the article.

So, why do you think the Supreme Court "just" interpreted the law?

What is the source of your incredulity?

Why should we think you - someone with "not much educat[ion]" in this topic - are credible? Why do you think your opinion is interesting enough to want to share?