The best answer here is that throughput has increased because one team member’s productivity has increased, which could be a cause of the other answers in this question. Adding more team members or outsourcing a piece of the project are
just two of the many possible reasons for an increase in throughput. The other responses are incorrect: testing could still go well with velocity being affected; development could still be efficient and productivity not increase; iterations
can be accurately estimated, but productivity meets the estimate.