Warden will turn hostile when there should be no reason to

I've noticed that wardens will turn hostile, even when there should be no reason to.

What I expected to happen was...

 Warden to wander underneath without turning hostile.

What actually happened was...

Warden turned hostile even if no vibrations occur post summon

Steps to reproduce:
1) Pillar up with wool, making sure there are no ways up.
2) Summon a warden below, via a shrieker, egg, or command
3) Make absolutely no vibrations.
4) Observe as it turns hostile against player

Clip:

https://youtu.be/4cE2Z2fQ44Y