It looks like one user was awarded the silver code-golf badge twice at the same time.
Their badges page also shows the badge being awarded twice:
This looks like a bug. It could be that Lyxal messed something up by traveling in time to get it twice, but if it's happened to others, it may need to be fixed. On the other hand, this looks a benign bug, and it's not really hurting anyone.
Sorry, Lyxal. Blame ChartZ Belatedly, not me.