The causality is there. Humans are very much a "monkey see, monkey do" animal and whilst one person might limit their racist out pourings to Twatter, another person will see those Twatter comments and want a more physical way of expressing their intolerance. Hearing/seeing racism repeated frequently makes people accept it (it's also why companies run the same ads for year after year), and makes casual racism far more likely, so I can't think of a reason why a more racist environment wouldn't lead to more racist violence.
As a white anglo-saxon who suffered racism (both verbal and physical) at the hands of white vikings for 2 years of his youth, I have fought it the rest of my life. As a white anglo-saxon who is stuck in Brexit Britain, I am simultaneously angry at and ashamed of my genetic tribe.