EV's in general, due to battery chemistry, do have a risk of spontaneously combusting. This has been an issue with Lithium Ion batteries since they were introduced, it isn't new. Yes, conventional vehicles also catch fire, but this isn't due to a single factor like it is with EV's.
If we look at the use of lithium ion batteries in grid storage, it tells a tale. So far, we have only a handful of large grid storage projects out there. Four of them have caught fire. In fact the one site has caught fire twice, once on the first phase of the install, the second on the second phase quite recently. This is not a good record for commercial grid storage using Lithium Ion batteries and it also calls into question how things are going to look as these age, as issues with these batteries increase with age and these were all quite new installs.