That BBC report also has a quote from an adjacent passenger suggesting that it was the seat and not a charger or phone that started the fire.
Having said that, I've lost count of the number of phones/chargers etc I've been asked to recover from seats. Usually business/first class where the owner has no idea it was lost until they try to find it after landing.
I even found a large tablet that was jamming one seat. We were called to fix the seat, the tablet had been 'mislaid' on a previous flight and not been reported!
Mind how you go.