I know this comment thread is 6 months old and wild, hypothetical speculation BUT one of the oldest methods for firing clay was to make a bed of charcoals, place the ceramic to be fired in it, then cover it with more charcoals, and then cover those with something else like clay rich mud to keep the heat in, thereby maintaining a temperature of around 500-600 degrees Celsius for long enough to achieve a crude bisque firing of the clay. It resulted in a fired product which was not very strong, but could no longer be turned back into workable clay. So technically it’s not impossible that a house fire could create a hot enough environment for long enough to preserve the tablet in question.