Perhaps the 700,000 demonstrators today are FSB plants as well
The Washington Post is the most toxic paper in the US and the English-speaking world in general on Russia so this was only to be expected. That sort of reputation takes hard work every day. WaPo's editorial board has joined the Spanish centralist press in denouncing Russia for "support of the separatists" in Catalonia:
"...the Catalan nationalists’ only backers are separatist-ruled Scotland, the pariah government of Venezuela and Russia’s intelligence and propaganda apparatus, which mobilized its media outlets and social media bots in support of the separatists. Moscow evidently perceives the Catalan movement as another vehicle for dividing and weakening the democratic West."
No evidence is provided that Russia cares an iota about Catalonia one way or the other, but it's not like evidence is required for claims concerning Russia.
Demonstrating its paranoia anything that WaPo doesn't like is—not just proclaimed a "victory" for Russia—but pinned on Russia's "intelligence and propaganda apparatus".
Madrid's police is busting heads, Barcelona politicians want to secede on a referendum with a turnout of 40%, and Washington and Brussels are embarrassing themselves with statements against popular self-determination — so this is all naturally Russia's fault.