Round musket balls in hand packed smooth bore dueling pistols at 20 paces is inherently inaccurate - ten shots in a row from a pistol clamped in a vise will have a spread greater than the profile of an oppenent staning sideways.

Bullets with rifling came about circa 1820 (ish) but were not widespread by 1832 and traditional dueling pistols remained the norm for quite some time, the element of chance likely factored in as part of the hand of god influencing outcomes.

https://en.wikipedia.org/wiki/Duelling_pistol

    For some in the eighteenth century, duelling with less-accurate, smooth-bore weapons was preferred as they viewed it as allowing the judgement of God to take a role in deciding the outcome of the encounter.

There's not a lot of detail regarding the duel of Galois, his opponent isn't known for certain, nor the precise reasons, let alone the type of guns and ammunition used.