That's interesting speculation; however, all the code that I've seen, in various parts of the documentation, has:

use FindBin;
use lib "$FindBin::Bin/../lib";
[download]

Yes, it could be legacy code: https://github.com/PerlDancer/Dancer2/tree/master/share/skel indicates .dancer was added five years ago.

If I come across any other information, I'll post it. Thanks for your attempts to help with this.