Also see perlsub in general and Prototypes in particular.

Those aren't arguments, they're prototypes

perldoc -f sub

sub NAME BLOCK
sub NAME (PROTO) BLOCK
sub NAME : ATTRS BLOCK
sub NAME (PROTO) : ATTRS BLOCK
        This is subroutine definition, not a real function *per se*.
        Without a BLOCK it's just a forward declaration. Without a NAME,
        it's an anonymous function declaration, and does actually return
        a value: the CODE ref of the closure you just created.

        See perlsub and perlref for details about subroutines and
        references, and attributes and Attribute::Handlers for more
        information about attributes.

They are subroutines, I just didn't bother to copy and paste the whole code

Reread what he said.

Arguments are what you pass to a subroutine. They're not being passed to the subroutine as you said. They're part of the subroutine's declaration.

I'll elaborate

sub fudge($){ print @_ }
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that is a function declaration -- it doesn't print anything

fudge(1);
fudge 2;
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those are function calls, it prints 1 then prints 2

If you wrote

fudge 1,2;
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the prototype ($) ensures fudge only gets 1 argument

If you try to force the issue with

fudge(1,2);
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You'll get an error

$ perl  -le " sub fudge($){print @_}  fudge(1,2);
Too many arguments for main::fudge at -e line 1, near "2)"
Execution of -e aborted due to compilation errors.
[download]

Next time, when you get links, follow them, read them, its what we all do :)

Sub prototypes were an experiment in Perl, and most experienced Perlers seen to agree we'd better classify it under the "mostly failed experiments".

See my archived copy of Tom Christiansen's old (but excellent and still very relevant) comprehensive article about prototypes, in FMTEYEWTK about prototypes.

(rolling his eyes...)   It is not the most intuitive syntax in the known universe ... but it’s what made the cut, and it does work.