The study looked at common, underlying psychological and behavioral factors that explain, at least partially, the genetics of both early sexuality and poor health trajectories. The strongest factors explaining the correlation being physical weakness, poorer mental health, ADHD-related traits (such as impulsivity), and lung diseases associated with early smoking. Early puberty + behavioral/psychological.
Age of virginity loss is also only about 25 percent genetic. No one is claiming a loss of virginity gene or that the connection is directly caused by the sexual event itself.
You didn’t read the conclusion either. Again for the stupid here - this is statistical nonsense being dressed up as “science”. They sliced and diced a ton of numbers to come up with an titillating conclusion they could make a paper on.