I don't think the Boston Marathon attack is perhaps the best metric to use. Yes, it matches the trend, but it's also an incident at a high-profile, yearly event and saw many injuries. By its very nature, it's gonna have much more coverage, eyewitnesses, and available footage and photos than, say, the Dylan Roof shooting.
That's not to discount the findings, just that the Boston Marathon bombing is a unique case. I have no doubt that media goes in harder on Muslim-led attacks than those by other religions or ethnicities.
