Could it be that the author uses the XS PREFIX keyword in his code? From perlxs

The PREFIX Keyword

The PREFIX keyword designates prefixes which should be removed from the Perl function names. If the C function is rpcb_gettime() and the PREFIX value is rpcb_ then Perl will see this function as gettime().

This keyword should follow the PACKAGE keyword when used. If PACKAGE is not used then PREFIX should follow the MODULE keyword.

     MODULE = RPC  PREFIX = rpc_

     MODULE = RPC  PACKAGE = RPCB  PREFIX = rpcb_
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