Caution: this post has nothing to do with the legal case of interest; it discusses only some obscure legal terminology.
"The opinion came down as part of a writ of certiorari"
That is not quite correct, although it's easy to see how the title page of the Supreme Court opinion (https://ancillary-proxy.atarimworker.io?url=https%3A%2F%2Fwww.supremecourt.gov%2Fopinions%2F19pdf%2F18-877_dc8f.pdf) could be misleading. That page contains, "CERTIORARI TO THE UNITED STATES COURT OF APPEALS FOR THE FOURTH CIRCUIT." That means that the Supreme Court agreed to review a case decided by the Court of Appeals for the Fourth CIrcuit. The document containing that annotation is the resulting opinion of the Supreme Court. The opinion is not really "part of" the writ. The writ was previously issued by the Supreme Court when it decided to take the case: as a result of its deciding to take the case, the Supreme Court sent a message, the writ, to the Fourth Circuit court saying, in paraphrase, Hey, we're going to review this case you decided so send us all the documents and records you have on it. That happened many months ago. Yesterday the Supreme Court "handed down" the result of its review in the form of an opinion written by Justice Kagan for the Court.
When the loser of an appeal in a U.S. Circuit Court of Appeals, or the highest court of a state, wants to appeal to the U.S. Supreme Court, the loser applies to the U.S. Supreme Court for a Writ of Certiorari, informally called an application for "cert," to be issued. If the Supreme Court takes the case, it "issues cert," and if it doesn't, it "denies cert." The Supreme Court issues cert for around one percent of the applications it gets.