Maria was a horrible storm and the death rate went up, but determining how many were really caused by Maria is a matter of judgement.

For example, death rates go up in winter. I could not find statistics for the US, but in Britain they estimate that even a mild winter results in 43000 extra deaths, mainly among the elderly. The numbers in the US could be several times higher given the larger population and more severe climate. By this logic, normal winter storms kill tens of thousands of people.