Well first, in what you posted it wasn't point blank. The fuel had to hit the "magma below". Second, turning the right way would prevent the fire from seeping through the front crack. Finally, once more his cape was completely undamaged which would suggest he actually found a way to shield himself from the brunt of the explosion.
True. Grievous probably used his grapple hook to get out of the facility that was completely and utterly engulfed in flames, and then went back into the facility to get a badass panel of him crawling out for the comic.
It can't of just been his armor that allowed him to survive the explosion.
__________________ “The galaxy must experience the pain of death and the rapture of rebirth as I have. I will bring chaos. It is time for war.”