Something worth noting.

Oils generally do not explosively combust. You guys probably know there's multiple types of explosives and methods for ignition. Some things require electric shock, others require extreme compression, others simple heat, etc. For example, gasoline/petrol itself doesn't explode when ignited, the vapors are what have explosive properties.

The kinds of oils available to the ancient greeks would not "explode", but they'd readily burn to varying degrees. They had manufactured oils such as plant extracts, and natural petroleum and derivatives were well known (such as bitumen, tars, oil shales and sands, etc). Consider that one of the uses of oil as a lamp fuel would depend on the fuel burning more slowly, not faster. This is of course also a function of the container or vessel's shape used as a lamp, but generally the oil itself would be more desirable the slower and more steadily it burned.

Bottom line, I still completely agree that having a bunch of flaming oil dumped into the middle of a formation would be a surefire way to cause some real chaos and panic, but I still maintain that as a weapon fire-based personal arms would be more trouble and danger than they're worth.