People are also pretty uncompressible. Ear drum damage is usually the limit of damage from the pressure wave from a gas explosion. (Of course the heat can cause burns too, as in this case unfortunately, and flying debris and building collapse can cause injuries too, although fortunately not in this case.) A small pressure wave exerts a large total force over a sealed surface such as a wall or floor, which is why they are less likely to survive.
Must have been quite a leak to build up to an explosive mixture. What you get out of a single gas burner generally can't get close if you assume anything near the norm of 2 air changes per hour.