I actually found that chest back in the early 90s. I think it was pure luck that I did it, of course.

It looks like a debug room because that's precisely what it was, albeit the entrance was added later as during development they'd just teleport there

Actually, that room was put in there by one programmer (I once heard Richard Garriot tell this story, I think in an interview with Noah "Spoony" Antwiler) without the rest of the team knowing. It was found by a playtester that found a bit of code in the middle of the mountains that shouldn't have been there (or something like that). Garriot had someone write a program to figure out where the teleporter was, and when they saw where the point of origin was, they were able to figure out who did it. It's also the reason that the "Cheater!" room exists (the one where Lord British declares you a cheater and sentences you to death), since they created that room and pointed the original teleporter to it, a little surprise for the programmer who put in the "debug" room.

my sister and/or I found it when we where kids(I was 9 she was 11)... I have the coordinates written down in a duotang of coordinates for stuff in the game we made at the time.

Also we somehow found the secret room on the blacksmith shop so given enough time and no internet to distract you apparently anything can be found lol

Same here. I was just messing around with all the crates, trying to make a staircase.