After reading the article, I think they didn't.
>"Both companies found that overweight or diabetic patients taking the drugs, called GLP-1s, had reduced biological age compared to those taking a placebo"
>“In an unhealthy population, I do think it’s an anti-aging drug, but in a healthy population, no one knows.”
Sounds like it's the already known "being overweight raises your biological age" and they're just acknowledging the inverse.