I too think he was sizing you up. He turned to his buddy and waited for the signal that you were no longer paying attention and wouldn't be expecting an attack. Moving the can was a little weird, but he may have had a brain fart and decided to do anything to make you think he wasn't just a weird guy and make you call the cops, which you should have done anyways. Its their job to investigate suspicious activity of any kind. If you've ever listened to a police scanner, you'd know how much non-violent stuff they have to deal with.
Anyways, by keeping your eyes on them and your alert level high, you never gave them the chance. Good work!
On a side note, did you think through the decision about dousing a man with diesel who was actively smoking? I personally don't know how combustible that fuel is in the open, but you wouldn't want a dirty haired hippie weirdo running wildly around a gas station while ablaze.
