No, that doesn't really count as eugenics either. If avoiding avoidable birth defects is eugenics, then cleaning up "agent orange" or ddt residue, or dioxins is also "eugenics".
Eugenics was practiced around the world and was promoted by governments, and influential individuals and institutions. Its advocates regarded it as a social philosophy for the improvement of human hereditary traits through the promotion of higher reproduction of certain people and traits, and the reduction of reproduction of other people and traits.
Eugenics core idea is that "some" people have genes which are superior, whilst others have inferior genes. And we should favor the first group to breed, whilst discouraging the second group.
Anti-incest laws recognizes that
everyone has mutant recessive genes which are harmful if you have 2 copies. It's avoiding there being people with 2 copies of these genes, by spreading out the gene pool. There is nothing in the incest laws which actually facilitates elimination of the recessive genes or changes the mix of genes in the population.
In fact, if incest was encouraged, more people with those harmful genes would die out, because the symptoms of the bad genes would appear more often, thus culling the gene. Which would create a long-term change in the gene pool, hence eugenics. The ban on incest doesn't reduce the amount of recessive genes, it just hides their negative effect, which effectively stops them from being weeded out.