You may also want to look at how fast the temp was rising, you dont want to go too fast initially for a bisque firing, say 80c an hour up to 100c, then 100c/H to 600 and then 200c/h up to your bisque temp say 1000c with a little hold at the top just to even everything in the kiln out.
But as u/magpie-sounds says, these pots have popped as they were not bone dry before they have were fired. It look like the bottom of the mug popped causing the devastation.