If you read the article carefully you will find that there was a period of three months between the earthquake happening and the actual volunteer construction work by the JWs. This delay would have allowed for insurance assessors to process any claims. Insurance companies in Japan do not repair or rebuild your home, you have to organize it yourself and as work is completed make the claim for the value of the work.
This then begs the question: Who received the insurance money for the value of the labor? Was it the JW volunteers? No, they were volunteers. Was it the JW home owner? Yes. Did tbe JW home owner have to pay the JW volunteers? No.