It is counting alcohol related deaths, not deaths from substitution effect to other intoxicants.
Alcoholism is unusual among addictions in that it's (1) largely invisible until its end state and (2) minimally taboo when it occurs in "high-functioning" individuals. Huffing chemicals is neither of those things, nor is swallowing mouthwash (which is more likely to make you sick than drunk at the quantities an average adult would need.)