It was not in Oct 2020 - it was on the 20th of October.
If the post would have been made in Oct 2020 it would have shown as Oct '20 (note the apostrophe).
In case of doubt, hover your mouse over the date and it will show “normally”
Selection of previous complaints about this in the past 10 years
- Displaying dates of posts - mixed formats make it hard to read
- UX: Date notation
- Post date display
- Part of the first (now deleted) discussion here.
Primary takeaway
It’s okay because Discourse was built for the future. And in 20 years, no one will confuse the years with the days because it’ll be Jan '35.
If only we weren’t merely in the pesky two thousand teens right now.
But there is also a solution: Post date display - #2 by Don