This is not entirely true.
Some patients have overactive or “hyperdynamic” muscles, particularly the frown muscles causing vertical frown lines. If they do not relax these muscles, they will ultimately develop “static” lines which cannot be completely treated with Botox.
These patients, if treated with Botox before they form static lines, will have effectively prevented them from forming. So for this group of patients, it is true that Botox will prevent some static lines from forming.
This is the mechanism by which this wrinkle-prevention benefit is achieved, it is not by any specific quality of Botox treatment in itself.