Reminders app showing wrong day, or may be its confused between 1985 and 2085
If you look at the date-entering form, you'll see that Reminders gives you space to write a 4-digit year, so it assumes the number you enter is the complete year. You didn't send it to 2085 – you sent it to 0085! (And because I have no life, I actually scrolled through iOS Calendar to check. 2/1/85 was, in fact, a Thursday!)

I don't know if a solution exists. You may just have to get used to writing the full year, or just clicking the date on the dropdown calendar.