I think that's a combination of high winds and young growth. If it is young growth, it's actually illustrating what the article is describing, the young growth trees are young, but not at young s they should be, and they bridge the gap between the undergrowth and canopy. Once the canopy catches in a dense forest, there's a real problem, but a dense forest with undergrowth only on file may be a mild, slow moving (since the wind may be mostly blocked) fire.