Why is my home owners insurance company(auto owners) sending out an Fire investigator ?

The Fire Dept already determined the cause.

Three possible reasons:

1) It’s just a random check.

2) They don’t agree with the Fire Investigator’s determination or somehow suspect it’s inaccurate or incorrect.

3) The Fire Investigator didn’t answer a question they have. (For example, he may have determined the location but not the source, or identified the source as an electronic device but not provided specifics about what the device is.)

They may be looking for someone to hold responsible. For example, if the cause was electrical, they may want to try to collect from the manufacturer of the device.