I am uncertain what pottu kasu is. Google translates it as 'spud benefits'. A Reddit commentator transliterates it as pattu kasu or padi kasulu and translates it as 'ten cents'. A sovereign weights 8g and these coins were 1/20 that so perhaps the coins are gold fanams.
The coins were discovered by accident by workers digging a septic tank. The report focuses not on the coins, but on how the finders attempted to divide and keep the coins.
Periyannan took the metal box and broke it in the presence of the farmer. To their surprise, they found small gold-like coins. They believed that someone might have buried the metal box with coins after performing rituals to ward off evil spirits. The farmer transferred the coins to a plastic container and kept it in his house. ...The worker along with Kabilan and another person reached Murugan's house and demanded their share. Murugan came forward to hand over the entire treasure to them but the worker and others took only 43 coins ...
Meanwhile, Ramasamy's wife Anjalai reached Periyannan's house and created a ruckus when she learned that he had got a share of the coins while her husband had not. The news soon spread in the village and the villagers informed the police.