He's pedantically correcting the poster who said "NASA were able to land humans on the moon 55 years ago". The first moon landing was July 20, 1969, so 54 years and 193 days ago.
To be fair to jaquesm, it looks like nanna's comment used to say '80 years ago' and was edited, so the correction was more significant. See comment by kitd.
That depends on how you're rounding. Human age is always rounded downwards, but with general timeranges, it differs. 193 days is 52.8% of a year (52.7% of a leap year), so you can round that to 55.