Is free() zeroing out memory?

Question

Until today I lived in belief that calling free() on memory space releases it for further allocation without any other modifications. Especially, considering th

Answer 1

is there a better explanation?

There is. Dereferencing a pointer after it has been free()d results in undefined behavior, so the implementation has the permission to do anything it pleases, including the act of tricking you into believing that the memory region has been filled with zeroes.