In a nutshell, __init__.py carries a comment which says:
# This code is original from jsmin by Douglas Crockford, it was translated to
# Python by Baruch Even. It was rewritten by Dave St.Germain for speed.
The original jsmin code is under the infamous Douglas Crockford license, which makes it non-free.
There is currently a discussion about this package going on in the debian-legal mailing list: https://lists.debian.org/debian-legal/2015/04/msg00032.html
Also, Redhat has rejected the package previously: https://bugzilla.redhat.com/show_bug.cgi?id=1014607#c10
Not sure what this means for this package. Looks like it went through two rounds of rewrites, and has also been reimplemented in a different programming language, namely python instead of the original js. Generally, an algorithm (an idea) is not protected by copyright, but only its implementation (a concrete expression of this idea). So one may doubt if the original copyright would still apply to it.
Disclaimer: IANAL, TINLA.
(In reply to Ulrich Müller from comment #0)
> [...] python instead of the original js.
Actually, the original implementation is in C.
The two implementations can be seen here: