Man-man-k-use-anchor is a variable defined in `man.el'.
Its value is
(gnu/linux gnu/kfreebsd)

If non-nil prepend ^ to the prefix passed to "man -k" for completion.
The value should be nil if "man -k ^PREFIX" may omit some man
pages whose names start with PREFIX.

Currently, the default value depends on `system-type' and is
non-nil where the standard man programs are known to behave
properly. Setting the value to nil always gives correct results
but computing the list of completions may take a bit longer.