Yes, but frozen potatoes don’t catch fire unless there is another fire to melt the cardboard boxes. Then maybe as the potato’s burn, it releases the starches that burn?
Since these were processed i expect there is a lot of vegetable oil in them from the making of ‘curly fries.’ The fact that there is probably a low potato to air ratio in packed curly fries (as opposed to raw potatoes) might help the burning also.
My guess - the fries were already partially cooked and had some oil on them already.