Spontaneous human combustion is the idea that under some very unique conditions, humans can simply ignite into ball of flames. This is largely not believed to be possible, and all cases of it seem to have simpler explanations (like them having a heart attack while smoking and having a brandy. Someone has the heart attack, spills the brandy on themselves, dies which causes the cigar to fall out of their mouth onto the brandy.)
Just being flammable means that if you try to use a blowtorch (or a match) to light someone on fire, you could do it. Human beings do burn like anything else biological, but it requires an external source of fuel (gasoline for example.)