It is a runway veer off. That's all we know for certain as of now.
the fact that it is Katmandu and that there was low visibility might not be related with it, although of course it can be.
They can have touched down on the runway normally (after Katmandu and lo vis) and only then they veered off. It can be related to the approach or not.
Everyone has a guess and thinks any other theory makes no sense, but I have been wrong about other cases so often, even when they seemed so clear that I can't trust any theories until we know more.
My theory now would be: unstable approach, hard landing, tyre burst, veer off.