No, I have a different theory.
See, judging from the police presence, I wasn't the only one expecting things to be much, much worse in Cleveland. At the RNC, I saw cops from Texas, Tennessee, California, both Virginias, and many more states. So far in Philadelphia, I've only seen Philly cops. On my last night in Cleveland for the RNC, I spotted four protesters playing a game of duck-duck-goose, surrounded by dozens and dozens of police officers.
Maybe the cops thought they were about to play Duck Duck Armed Robbery?
As I left, I met two-dozen highway patrol officers all rushing in to this dangerous Duck-Duck-Goose-In. I said, "I think your buddies have it handled," and got sheepish, almost embarrassed smiles in response.
There is a school of thought that hyper-aggressive policing can actually trigger violence in crowds (the Justice Department says this is one reason the Ferguson protests got out of hand). From what I saw on the ground, I'm now convinced this was part of it. No, this isn't blaming the police -- they're trying to keep everyone safe. But there are elements of crowd psychology that come into play here.
The most violent, and frightening, the RNC ever got was when these assholes showed up: