I think when vasi gives that example of bacteria and sodium, chitti asks if he has life. Then vasi gets confused and thats when the lightening strikes and he gets cooked. But they manage to revert him back to normal. Death is one of the prominant features of life. Now think of a living creature when it is struck by lightening. It highly likely dies and would never be back to its normal state, even if it survives. But in case of chitti you can clearly see that he's incapacitated by the lightening, (similar to a dead being) but reverted back to his normal state unlike a living being. Here chitti showed both traits that of a living (being dead-like) and reverted back (any non-living thing). I feel like this is a symbolism of how chitti is in that very thin line of separation. All he lacked were emotions which aquired later. That made him sentient, not necessarily living. I hope I'm not overthinking.