I come from a family of pyromaniacs. I was just an amateur, but my brother became a fire fighter and then a fire marshal.
As other people said, pine trees burn really well. Once, as a scout, our troop participated in a fire building contest. Usually contests involved boiling water, but that one was was simply to burn a rope about two feet off the ground. We were given a couple of minutes for prep time and then they rang a bell for the troops to start their fires. We were given three matches, but everything else was to be gathered there in the woods. Axes and saws were permitted.
As our troop’s fire expert, I told the other guys to forget getting any sticks, logs or even twigs. Just get as many dry pine needles as possible. Six guys racing with handfuls of pine needles can collect quite a pile in three minutes.
They gave the warning, the bell sounded, I lit a match, poof, a fireball and we won.
Yes, rooms can go up like that. My brother’s fire department burned a number of homes for training. People would let them burn old houses which were scheduled to be demolished.
There are many youtube videos showing flashover. Here’s one showing a side-by-side comparison with a “legacy room” vs. a “modern room.” The modern room has flashover in less than four minutes while the legacy one takes almost 30. There really isn’t enough information to know what materials they use, but one to two minutes could be expected with a pine tree setting it off.