Yes, "cold as clay" is misleading, particularly given the associations of "clay" with death (symbolically, the substance of a lifeless body, as well as what a body is often laid in, according to many songs), not to mention the obvious association of
"cold" with death. However, we do have the expression "out cold" to indicate unconsciousness, accompanied by, presumably, lowered body temperature.

Just looked up at Mick's post again, and notice that he in fact used the expression "out cold" ...