I think you are getting that the elements are dispersed by the explosion. Not that they elements were formed during the explosion.
But it does not say anywhere that this is in exclusivity. Yes, some amount of nuclear fusion (the process that forms these elements) that happens during the explosion, but the process is on going. The larger the star, the heavier the gravity. The heavier the gravity, the more the atoms/etc... are smooshed together. The more they are pushed together, they form heavier and heavier atoms.
The explosion is what forms the heavier elements. Energies that are far in excess of what a star can produce during it's 'normal' status is simply unable to produce temperatures and pressures high enough to even 'kill itself' producing anything heavier than iron.
In the supernova, things are different, but to say that that's a product of the star's normal fuel-burning process is, well, wrong. The supernova is what happens when the star is OUT of fuel to burn. This energy can come about as the entire star comes crashing in on itself, but that's not part of the "burning process" that describes other elemental fusion processes.
The thing is, no star can fuse anything in a normal burning process into elements heavier than nickel, no matter how big it is. The nickel itself can eventually turn into more usable fuel, but the half-life of this process is about a week long, and the star simply cannot wait that long, no matter the size.
The reason for this is that a star isn't going to fuse heavier elements while it still has fuel in lighter ones, because it's not hot enough. Once it runs out of almost all its fuel, it contracts, increasing temperatures and pressures, and the next stage of fusion begins. So a star will have all this iron floating around doing nothing, until it's almost completely out of chromium, then it'll burn iron. Once it's out of iron, it'll try to burn nickel, but begins to exponentially drain itself dry, and in MINUTES, the star is dead.
Then it collapses in on itself, and in a brief moment, once all of its mass is concentrated on the core, in the rebound, it'll begin an extremely hot, rapid fusion of everything that is inside it, producing heavier elements, which are blown off in the ensuing explosion. Everything that is left, however, is smashed into its component pieces into an ultra-dense blob of matter made of atomic components.
The problem is, they CAN'T fuse anything heavier than iron during their lifetime, because the half-lives of the isotopes are longer than the duration of the star's life.
Effectively, while a star COULD spend more of its 'living' energy fusing iron into heavier elements, it is simply unable to do so with the
