Indeed - it uses the zmalloc code. Here, a little excerpt from the comment at the top of zmalloc.h:
This code was not part of the original CircleMUD distribution. It has been
included in tbaMUD and is attributed to:
Version 1.1 Copyright 1996, 1998, 1999, 2000 Eric Murray ericm@lne.com
Note that the code in tbamud isn't an exact copy of Eric's code, but is derived from his example.