FC Barcelona is one of the main symbols of Catalonia and the push for independence or increased autonomy.
Click to watch video hosted on YouTube. Russia has its own issues with regions like Abkhazia, Krim, Caucasus. Thus not surpricing with a bit of support from Russian side.
The colors of the Catalan flag are often part of the design of jersey, apparel, and merchandise.
For many years the jerseys of Barca were void of any kind of commercial influence apart from a small badge on the left arm sleeve for the Catalan TV station TV3.