Smaller also means cheaper.
There wont be steam explosion (which is what Chernobyl incident boils down to)
I am not even taking into account that Chernobyl depended on engineering to not blow up, but gas reactor produces less energy if fuel becomes hotter due to the physics.
Triso is safer because we wrap the fuel, only the wrappers will melt/fracture at the temperatures we know may occur at the exact time we need them not to melt/fracture. So we might as well not bother right?
Chernobyl occured because of graphite/fuel configuration went wrong. In this fuel it just cannot go wrong as it never changes.
As for temperature being too hot, pebble reactors have a so called melt-plug, which will melt at temperatures much lower than would be threaten the pebbles
Once the plug melts, pebbles fall down via gravity into lower part of reactor where they are dispersed in a way that stops energy generation and they can be cooled by natural convection.
Walkaway-safe is huge deal. You can't overheat this reactor even if you set out to do so.