The death anniversary is more significant than the birthday anniversary.
OP is commemorating that.
Hindus believe in a reincarnation cycle of birth, death and rebirth. Traditionally, when the soul departs the physical body at death, it needs to move to an astral plane to await its next reincarnation. This plane is said to be populated by the three preceding generations of the deceased individual (See Reference 1, Page 61). When the newly deceased enters the plane, the oldest preceding generation moves onto their rebirth. Immediately after death, the individual’s soul is believed to linger around its living family and may cause them harm until the shraddha rites are performed, letting the soul move onto the astral plane (See Reference 3, Page 59).
Immediate Shraddha Service
In the days immediately after death, families gather for a large meal in celebration of the deceased. They generally offer rice balls (pinda) to the dead family member, who is often represented by a photograph. Then a Hindu priest offers four rice balls as well. One is large and represents the recently deceased while the other three are small and represent the preceding generations awaiting reincarnation. The large ball is divided and combined with the smaller pieces, symbolizing how the deceased is reunited with their ancestors. The rice is then fed to either crows, a cow or fish.
Annual Shraddha Service
The annual shraddha service in homage to the deceased is similar to the rites conducted immediately after death.
https://classroom.synonym.com/the-anniversary-death-ritual-of-hinduism-12086888.html