The cheap Chinese batteries are a different chemistry, lithium iron phosphate, that's way safer than Tesla's lithium cobalt batteries.

There've been many Tesla garage and spontaneous fires, although not a big percentage of cars sold. So an individual's Tesla is not likely to catch fire in their garage, but given the severity of it happening you'd be a fool to not park it outside.

edit: Tesla is recently starting to also use iron phosphate batteries so hopefully fewer fires.

There are literally billions of Li-ion batteries in the world. While this is scary, it is exceedingly rare when you consider how many there are in use