The opposite of open source is closed source/proprietary, not commercial.

Essentially true, even though "Opposite" isn't the term I'll use here, as there are several approaches to open source, free software, closed source and proprietary.

...everything can be uploaded to CPAN as long as it is freely distributable...

From the CPAN FAQ:

Does CPAN allow contributions of shareware or code that requests a fee of any kind?

No. Everything on CPAN is free of charge.

As for the licensing itself, there isn't any reference to what license you *should* release under, only that most are released under either the Artistic or the GPL licence.