I want to know why the cat in this video: https://youtu.be/WdbB_6mlCPw?t=521 is making this sound. Is a particular meow of that breed or...?
It's not breed dependent. The cat is terrified in this video.
The ears pasted back on the head, wide eyes, swishing tail, hair fluffed up are all signs of fear based aggression.
The sound is how distressed the cat is. Trying to warn the mannequin head to go away. This sound is not breed specific, but behavioural specific. There's variation between the sounds cat's make, as there's variation in the colour of their fur.