The legal proposition given is that whoever causes death by an act with the intention and the knowledge that he is likely to cause death.
Since in the legal principle the word 'and' is used instead of 'or' therefore, intention is essential with the knowledge that 'the act' is likely to cause death.
'Y' did not have any intention of causing the death of 'X', this can be proved by the fact that Y fired a shot at the bush under the presumption that it was an animal .
Thus with an intention to kill an animal and not X.
Therefore Y has not committed culpable Homicide.