Social workers and ER nurses, in particular, have field-tested practices for dealing with people who are anxiously disoriented — or violently psychotic - in a manner which resolves the situation peacefully.

All I can say for what I did at the time was an intuition that I was confronted with a half-tranquilized, large confused ape and so acted as to prevent them from panicking and running amok with calm words, movements, and (most importantly I suspect in that state) caring touch.