To clarify why it's "that way":

You actually are using Inline, with the C plugin. So "C" is an argument passed to Inline similar to how a function name might be specified in an import list.

The reason it's often seen "bare" is because it's quite common to do it this way:

use Inline C => 'DATA';

# ...

__DATA__
__C__
/* C code here */
[download]

In which case the "C" is actually quoted by the fat comma (=>) operator.

Multiple uses of Inline C =>... are common and ok; one is often used to specify configuration settings, while others are used to initiate inline code sequences either via a here-doc or the __DATA__ segment.