I think the reality of that statement means that we all have a genetic potential/ceiling but most if not all of us exist way below that if we are talking about hypertrophy and strength. That doesn't stop us from trying to get there though (with or without chemical assistance).
This is basic, so that it can be understood;
We are born with a set ratio (cannot be changed) or percentage of fast and slow twitch fibers in a particular muscle, out of the thousands of muscles supporting the skeleton and circulation the % of fast and slow twitch fibers will differ not only from one person to the next but from one muscle to the next of an individual.
The reality is, genetics play a huge role, and it is not just one thing, others factor include muscle belly size;
The calf muscles contribute little or nothing to either running or jumping, serve primarily as shock absorbers; you
cannot jump high enough to even get your feet off the floor while using only your calf muscles.
When running you first throw your lower leg out in front of you, using the quadriceps muscles (the front of the thighs) and the hip flexors, and
the calf muscles contribute absolutely nothing to that movement.
Then, when the involved foot is planted on the ground in front of you, the body is pulled forward towards the planted foot, that part of the movement being performed
primarily by the muscles of the buttocks, again with no meaningful contribution of the calf muscles.
Thus an increase in size, and the weight, of the calf muscles would make it harder for you to throw the lower leg as far
or as fast as you could with smaller calf muscles. So you would be slower rather than faster.