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:
They have a certain range where they can detect you via sniffing if you're too close to them, and their vertical radius range for sniffing is larger than the horizontal, so you probably were within that range.