Have I got it all wrong?

No, the demo is fudgy :) and fudgedocumented :)

But, if you UTSL like I did, you can see that you need to run perldoc -MModulino::Demo3 Modulino::Demo3 to see the magic, quite fudgy indeed

Also it works with perldoc -MModulino::Demo2 Modulino::Demo2

This will run the tests  prove -MModulino::Demo

So you can see, some of these things just aren't that well thought out

FWIW, here is background on brian d foy modulino stuff
How a script becomes a module
http://www.slideshare.net/brian_d_foy/advanced-modulinos-trial, http://www.slideshare.net/brian_d_foy/advanced-modulinos

Programs as modules is great idea, but this "run how its loaded" is bleh at best
good idea connected to these bookmarks (module as code) is schwern's skimmable code