You're assuming something they didn't say. Genetics might mean a poorer response to GLP1, or a poorer metabolic response to specific hormones, or how we observe that people with ADHD have poorer eating habits, or if you're genetically smaller then your metabolism may be smaller, blah blah blah. There are many genetic factors that obviously impact weight.

We know that alcoholism is genetic, addition is genetic, etc, and those are just tiny subsets of problems that genetics are involved in.