Your fund "paid a dividend."
It handed back your own money.
0
Rupees of extra wealth an IDCW payout actually creates. The NAV drops by the exact amount it pays you.
Fund sitting at Rs 50 declares a Rs 5 IDCW. The NAV opens next day at Rs 45. Same units in your hand. Rs 45 of NAV plus Rs 5 of cash is still Rs 50. Nothing earned. But that Rs 5 just became a taxable event.