Working as Designed I don't think this is normal

[UNDEADTJ]

Single Player/Multiplayer

Single

Operating System

Windows 10

Controls Used

Keyboard/Mouse

I was just going through the dungeon on journey mode and I found this when I was looking in pre hard mode

 

[John Snail]

The Angry Bones are activating the Unicorn and Skeleton Statues in that room.

 

[Kazzymodus]

There are a Unicorn and a Skeleton statue in the bottom left pit. When activated by a pressure plate/wire, they will spawn Unicorns (even on pre-Hardmode) and Skeletons, so this is not a bug.