It could be arson and it could be just a failure in some
of the utilities, electrical, etc. Go to the following link
and you’ll see the structure of the top which is wood.
I suspect there are gas/electrical lines thru out . Thus
it could be some failure there.
I’d post a couple pictures but I can’t get the source info.
What do you expect?(sigh)
Electric wiring was more than 800 years old.