Yes they are spinning it for gravity.
For those who may want a brief synopisis. This is a small satellite manned (if you will
) by mice. It spins to simulate low gravity and the mice will be returned to Earth to evaluate any changes or damage caused by prolonged low gravity. That is low gravity not freefall.
They wish to answer the question, can people live in low gravity environments (the moon ~1/6th and Mars ~1/3rd) for prolonged periods? Right now people believe that we can colonize the Moon and Mars, but can we? Will the reduced gravity require people to return periodically to the Earth or have to use centrifuges to maintain health?