It was a concern for several people, primarily because they were bringing in lots of gasoline or diesel to a certain area. You want to make sure that it's being used for the purpose that it's supposed to be used for.
When you're thinking of a demonstration, there's always a possibility that those volatile liquids could be used for other things, like Molotov cocktails, or other types of weapons. You're never guaranteed that it's just going to be used to refill the....
That was the primary concern with the gas cans.