For some reason, the warden will play the sound "Warden Takes Notice" or "Warden Takes Notice Angerly" if touched in its death animation. If the warden dies without aggro, it seems to only play "Warden Takes Notice" but if it dies with aggro, it seems to only play "Warden Takes Notice Angerly".

To replicate this, kill a warden and walk into it while it is in its death animation. This will only work in survival as it cannot have aggro on you in creative. You could also use the following command to summon a warden in its death animation to walk into to see this bug in action.

/summon warden ~3 ~ ~ {Health:0,DeathTime:-200s}

This command will always make the warden play "Warden Takes Notice", but you can hit it once in survival and walk into it to see it play "Warden Takes Notice Angerly".