Great eye mx... I didn't see that until I read your post. That could be exactly what gave way. A piece of wood can't hold the weight of a truck. Most lifts have an end piece that can be flipped up and it's made of sturdy metal but it does look like this guy used a block of wood instead.
Once a friend and I used wood rounds (from a cut-up tree) to hold up a truck while we worked on the transmission. The wood splintered and the truck crashed down and stopped inches from our faces. *SHUDDER*