Right, the player was just an ordinary guy, probably not even from the submachine world.

To me, I think is it likely that the person were "somehow" transported to the submachine world.

I know that's late, but happy birthday! Mr. Mateusz. Hope you have a great day there!

...when you sees a familiar device you believed were the dimension-traveling device.

ENIHCAMBUS: Not bad, however. What make thing look messy is the .jpg. No offense, though.
Gemini: Those are nice recreation of a table in the laboratory, I like.

..when you warped to The End in Minecraft (note: The End are take place in floating island in dark void)

Surfing through internet, that's all.

Happy birthday to Diamonds! Although I don't know who it is. By the way, have a good time!

..when you thinks a single leaf can warp you to other place.