It was not unusual that reporters on CNN and some other news stations stated that it was an accident, or related to the restoration work, within 30 minutes of reporting on the fire (see early discussion comments). As soon as something happens, everyone wants to speculate and, in some cases, irresponsibly state speculation and opinion as fact.
That does not mean that the official decision about the cause of fire was "accident" and that the investigation is concluded, but rather that reporters were doing what they always do. At this time, there is still no evidence of anything other than "accident," so reporters were correct in their speculation.
It seems a bit odd that there is criticism of the fire investigation on the basis that USA media speculated on the cause of the fire as soon as they learned about the fire.
Trump had lots to say about putting out the fire, tweeting that tons of water should be dumped on the fire from the air. The French had to post a tweet in English to address the "lost in translation" issues so he could understand the serious damage that would result from dumping tons of water on such an old building. There were all sorts of pseudo experts on the other side of the pond telling the French how it is and what to do.