With all due respect to your year of con law and semester of criminal procedure, I think I'll take the word of the Sanford Chief of Police and the city of Sanford; an official explanation is front and center on their web site specifically addressing why he was NOT arrested here: http://www.sanfordfl.gov/index.html.
It clearly states:
It doesn't say that he wasn't charged, it says that he wasn't ARRESTED. According to this sources, and countless others, he was NOT arrested, and I would presume that Sanford PD has more accurate information on that than just an assumption that handcuffs equal an arrest.
I agree, either gitana is correct that he was arrested and SPD is lying about him being arrested or he really wasn't. If they didn't mirandize him, they for sure are not going to say they 'arrested' him because it gets them into all sorts of hot water, he's basically testifying to the officers in the video.