I have never heard of Ray Hennessy. Do you mean that he said animal detection was more reliable on the Z9 when used to photograph birds than bird detection?
I have shot thousands of bird images with my Z 9's and from about firmware 4.0 (not sure exactly which one) on that bird is significantly better than animal for bird photography although animal does an ok job much of the time.
The Z6III is not bad in animal for birds but definitely not as good as the Z9 in bird. How much of that has to do with the subject detection settings and how much the Z9 I am not techie enough to say.
As
@Steve said in Z6III set up video and a few other times never be afraid to use the old bread and butter single point if other AF Area modes have a hiccup. I use that more with the Z6III than I do with Z9.
Update: I looked up Ray Hennessy and on his page he calls it eye tracking which is not a feature on Z9 or Z6III it is subject detection ... it bugs me when you tubers start out that way.