Please note: Washington had previously repeatedly warned about the preparation of a terrorist attack in Russia under a "foreign" (i.e., "Ukrainian") flag to create a narrative for general mobilization.
But!
Not this time.
Even though the US warned the Russians about the terrorist attack, they did not say that it was a provocation being prepared by the Russian security services themselves for the purpose of mobilization against Ukraine. So they didn't have that information, and that would indicate with a high probability that in this case, as Freud would say, "a terrorist attack is just a terrorist attack."
So we still have a chance to extinguish Russian outrage by channeling it into the ISIS-version, which appears to have a good chance of being true. If successful, this would be a big information problem for the Kremlin: it pours propaganda resources into anti-Ukrainian narratives, and suddenly they are interrupted by the image of Islamic radicals reborn from the heat.