u/Apprehensive-Pass-90

I haven't taken aby pictures yet, but I've found something I can only describe as an Enderman lair in the overworld? Its a little space in a natural mountain cave filled with Endermen and their dirt. They made a little house! I thought this was intentional espeially because the entrance was sealed with dirt and you could hear Endermen sounds coming from it. Has anyone ever seen something like this before? I'm a casual player, so I don't know much about intresting added things. I'll also add that the area is in general filled with Endermen for some reason.

Tldr: Endermen filled a little cave with dirt and live there