No, that's an implementation detail which isn't actually true of the associative arrays in all of these languages. "Associative array" is the name for the interface, not the implementation. In theory it could be a hash trie or something, although I'm not aware of any implementations of any of these languages that uses anything but a hash table (which is, yes, fundamentally dependent on using an array).
It doesn’t mean HTs are the arrays which should be used to store seqint-indexed values.