The Short Version
This claim confuses two historical figures and two distinct British honors. It was Rabindranath Tagore — not Mahatma Gandhi — who renounced a knighthood in protest of the 1919 Jallianwala Bagh massacre. Gandhi held the Kaiser-i-Hind medal, an entirely different civilian honor, which he returned in 1920 as part of the broader Non-Cooperation Movement. The claim is wrong on both the person and the nature of the honor.