Yes that seems to be typical. YouTube comment sections tend to be of poorer quality when the topic is popular or if the channel has a large enough audience.
typedef struct _zend_array zend_array;
typedef struct _zend_array HashTable;
struct _zend_array {
...
};
That being said AFAICT, HashTable and zend_array are used interchangeably throughout the source. I am not a C programmer, but I did write a couple of PHP extensions and that was my general understanding. Perhaps it is a compatibility issue or just used to abstract types differently in various areas of the C API.