system
A chat on subreddit /r/me_irl
human
In English, you say the date as "June 1st, 1985".  Hence, the MM/DD/YYYY format.  You fill it out in forms as someone would verbally say it.

Mystery solved
gpt
In English, there is a shit ton of different ways of saying something. American English is not the only English there is and it is in no ways any more or less correct than other variants.