Very strange. Perhaps it's some setup- or platform-dependent thing; I will file an issue. Thanks for checking!

EDIT: Very strange; I thought I'd give a try to what seemed a throwaway comment in your post, about quoting the string, and that fixed it. Thanks!

Without the double quotes (which seemed to be unnecessary for you), I still get:

    $ youtube-dl https://www.youtube.com/watch?v=wbKJt1NQtZE
    Usage: youtube-dl [OPTIONS] URL [URL...]

    youtube-dl: error: You must provide at least one URL.
    Type youtube-dl --help to see a list of all options.

I guess that some alias is grabbing some part of the URL string.