You can definitely implement malloc in C. It does nothing special in its most basic form but cough up void pointers into its own arena.
It gets complicated when you have virtual memory and an OS involved but even then you can override the system malloc with a simple implementation that allocates from a large static array.
No, returning parts of an array does not implement malloc as described in the standard. That's not a new memory object, it's a part of an existing one.
The standard is written to accommodate obsolete tagged memory architectures that require special support. They aren't relevant today and data pointers are fungible regardless of where they originate.
But in practice it's not always true on Apple A12 or later because they support PAC (so pointers of different type to the same address can be not equal bit-wise) and is even less true on very latest Android because it supports the really big gun MTE. And MTE is great; you don't want to miss out on it. No explainer here because there's no Wikipedia article for it(!).
Also becomes not true on any system if you use -fbounds-safety or some of the sanitizers.
It gets complicated when you have virtual memory and an OS involved but even then you can override the system malloc with a simple implementation that allocates from a large static array.