as far as I recall, it was his own power, just not under his own control.
he also has the ultimate nullifier which should nullify any argument (pun intended), and which did reset the whole universe, undoing what he'd wrought. but I was just using that for comic effect (pun, yet-again, intended).
but was the nature of that tampering sufficient to deny Galactus the feat?
anyway, it's not very likely that Galactus will be ending 616 any time soon... Marvel's X-men cashcows would be sunk if that happened, and he's not a popular enough character to merit his own comics and hoary old tales from back in the day when he used to get drunk with Phoenix at the pub and end the universe for laughs ... so, it's all we've got to go on, along with is job/place/function in the universe and the nature of his powers and their ability to consume anything and everything.
if we're agreed that it shows his potential, then the point is moot. this thread is regarding a Galactus at "100%".
though even going by the argument that it shows his potential, there is implicit the acceptance that the feat was an exercise of his powerset and not something beyond his reach, just not within the realms of his everyday showings.
Gender: Male Location: somewhere within time & space
We shouldn't forget yall,
the Black Celestial just made it impossible for Galactus to stop,
but Galactus was showing the capability to contain all that absorption.
According to Reed, all of 616's History would not be enough to satiate him.
According to the GOTG,
Galactus was indeed on his way to absorbing "all existence" ...
the dilemma is like Galan said,
can he make himself insatiable at will (we've never seen this)
But a greater question arrives,
would Galactus ever want to do that?
I say no.
Galactus defends Reality ... I'm sure he doesn't want it consumed,
also, Galactus is an integral part of Reality,
Galactus refers to Eternity as his Father,
Eternity refers to Galactus as his equal in status.
These simple reasons tells us,
it's unlikely we'll ever see Galactus make himself instatiable,
even if he could.