'7-15%' does not look like a lower bound to me.
I wonder if the resolution is that the first is supposed to read 'the ratio of Sun-like stars to Earth-sized planets orbiting such a star within its habitable zone is around 5:1'. That would double-count stars with two such planets.
'7-15%' does not look like a lower bound to me.
If there is uncertainty in the lower bound produced by an argument, how else would you write it?
On the abundance of extraterrestrial life after the Kepler mission Amri Wandel
Some recent calculation of the Drake Equation with estimates of the likelihood and logevitiy of civilizations
Related: The Great Filter and Planets in the habitable zone, the Drake Equation, and the Great Filter