First off they're not the same. Second, his sample is like 20 games so it's not that significant.
But if I had to guess, honestly it's probably that the bronze player doesn't even have the thought that he could use his spells and maybe get a kill. From what I've seen of most people in bronze, they just don't think.
The silver player can actually identify that he can use the spells, it occurs to him that he might have a kill, but he doesn't calculate for the enemy actions.
I like to describe the ranks like this.
In bronze, they have no idea what it should be
In silver, they know what it should look like but not why it happens
In gold, they know why it happens but not how to do it
In plat, they know how to do it but not when and where
In diamond, they know how, when, and where, but not always why.
masters and above fully understand the how, when, where, and why.