What this most likely means is that genes involved in alcohol/substance dependency are located on the same chromosome as genes that control eye color. When genes for different traits are located on the same chromosome, they are called “linked genes.” Other than the physical proximity, the genes have nothing to do with each other. Having green eyes does not cause alcoholism/substance abuse.
While there have often been claims of genetic predilections to alcohol/drug dependence there is no actual proof that such a gene exists.