You had advantage, as stated in the log. Advantage means you get the chance to roll twice (and take the better roll), so the percentages are adjusted accordingly.
You needed to roll a 9 with advantage, which is a 84% chance.
https://statmodeling.stat.columbia.edu/2014/07/12/dnd-5e-advantage-disadvantage-probability/If I were Larian I'd include an entertaining tutorial in the full, but that's not up to me.
