Or he stirred a lot of it up himself, making things racial that weren't. Along with much of the media. Trayvon Martin was made immediately about race with edited clips of the call to 911 to make it seem like that's why he was being targeted. The truth was much different. Don't let the truth get in the way of your great narrative though.
The truth is that no story about a situation like Trayvon Martin's can possibly be discussed in the south (or various other parts of the country where racial tension is high) without bringing race into it, because whether you say it out loud or not, a lot of people will be assuming that if Trayvon had been white it would have gone down differently. We can't know that for sure, of course.
FWIW, I think the verdict was the only possible one because George Zimmerman's claim that Trayvon had him on the ground and was slamming his head into the pavement wasn't contradicted by any evidence. That situation easily constitutes a deadly threat and justifies the use of deadly force in response. I'm less confident that Zimmerman's story was completely true, but it wasn't inconsistent with the physical evidence and there was no eyewitness testimony.
As for Obama's comments... all he said was that it was imperative that the case be investigated thoroughly, and then he made some sympathetic remarks to Trayvon's parents. How is that "stirring up" racial tension?
I should point out that I'm no fan of Barack Obama. As a conservative-leaning libertarian, I largely disagree with his political philosophy, and I think as a president (politics aside) he was mediocre at best. As a supposed constitutional scholar I was extremely disappointed with his handling of several really important issues related to the balance of power, especially his expansion of the already excessive power held by the executive. Bush did the country great damage by expanding that power dramatically, and Obama should have rolled it back but instead he pushed the pace.
However, even though I didn't like him and didn't agree with him, I see no substance to the argument that he "stirred up" racial tension. He acknowledged it, and at several points he expressed sympathy with the black community and acknowledged his own membership in that community, but that's all. Never did he introduce it where it wasn't already present, and never did he ignore the facts and assign blame based on race. If you have any examples to the contrary, I'd like to see them.