Yes. Sri Aurobindo is referring here to his experience in Alipore jail. But what is interesting in this aphorism is the contrast he points out between the material prison where only his body was confined, while his spirit, unfettered by social conventions and prejudice, free from all preconceived ideas and all doctrinaire limitations, had a direct and conscious contact with the Divine and a first revelation of the integral Yoga; and, on the other hand, the mental prison of narrow rules which excludes life" and within which people often confine themselves when they renounce ordinary existence in order to devote themselves to a spiritual life based on traditional dogmatic ideas. So Sri Aurobindo is here, as always, the champion of the real freedom beyond all rules and limitations, the total freedom of perfect union with the supreme and eternal Truth.