Compared to flammable liquid fires at 180,000 per year, see above, which really are pretty common.
This is a straw-man argument too. You're comparing battery fires to all vehicle fires. Ask any mechanic and they will tell you vehicle electronics systems are the primary source of crispness with stalled electric motors and rodent damage being the primary sources. Regardless of how it gets its motive power a vehicle's power-train rarely catches fire compared to other things that catch fire (which is probably in part why the NHTSA is interested in this).