Once again it's because the warning indicator is deciding weather or not you are to take damage/effects. Not the actual mechanics.

Seriously find a landslide that is not targeting you and run directly into it as the warning line disappears... Jump around in it, have a seat, dance a jig! You will not take damage!

However if you don't get away before that indicator disappears + 0.3 sec position update + server ping + hardware latency... You can be on the other side of the map and you're toast!

It's awesome it's like you have to escape the warning with a giant random vision debuff! But you can totally play around in the explosion no problem!