I noticed that too. The Optimus stove in question is supposedly dual-fuel (gas/kerosene). And some of the kerosene available in the third world (for example) is said to be really terrible, low-grade stuff.

A kerosene stove could likely handle paint thinner (even used and filtered).

And I've noticed that old oil paint will separate into pigment and a clear, oily liquid. If you could filter this stuff and maybe thin it out somewhat, it might work.