That is simply not true, unless you are shooting the bullet horizontally or toward the ground.
A bullet is slowing the instant it leaves the muzzle of my rifle when I shoot it straight up overhead. But that bullet is climbing until it isn't.
The bullet is certainly earthbound the instant it leaves my rifle...but it takes a while to begin to fall.
If nothing is still driving the bullet, it’s falling. Its upward momentum may cause it to get farther from the earth temporarily, but it is falling the whole time.