Here's some semi-random news articles regarding this:

https://www.nrk.no/livsstil/advarer-mot-oppvaskmaskin-om-nat...

https://www.nrk.no/osloogviken/bonn-fra-brannsjefen-i-fredri...

They know because they have to put out the fire in the middle of the night, and they do an investigation afterwards to determine the cause of the fire so they know it was e.g. the washing machine.

Presumably the fire department is merely offering advice, because they’ve been called out to dryer fires. And they’re the fire department, not the energy efficiency department.

You will be surprised how often disembarkations in the electrical space go hand in hand with a potential embarkation into the fire space.