I'm under the impression Roman siege engineering wasn't yet too hot around that time. Syracusan, on the other hand, was. Add in whatever weirdness Archie came up with, and I've no doubt the Italic rustics were generally in awe of actually fairly normal stuff.

Plus claiming the Syracusans had pretty much everything short of a machine gun would have been an useful face-saving excuse for the siege taking as long as it did.

Personally, I figure that if the Syracusans went and burned some Roman warships at range they just used normal incendiary weaponry. I've seen it mentioned fire-hoses occasionally popped up in Greece already before the Hellenic period, and assorted catapults make pretty decent delivery systems for something unpleasantly flaming. Assuming the Romans were unfamiliar with the idea they could right well have attributed it to pretty much anything up to and including divine intervention, or in this case Archie's infernal devices since the guy was presumably pretty famous and everyone knows them Greeks were way too cunning by half anyway.