Ruby version was based on the Perl version, and this author acknowledged his was based on those 2 versions (from the previous version's README):
faker.js was inspired by and has used data definitions from:
https://github.com/stympy/faker/ - Copyright (c) 2007-2010 Benjamin Curtis
http://search.cpan.org/~jasonk/Data-Faker-0.07/ - Copyright 2004-2005 by Jason Kohles
The Perl package is GPL. He took definitions from it, ported them to JS, and licensed them as MIT. "Is license violation theft?" is one of those questions like "Is piracy theft?", but it does undermine his insistence that he should be allowed commercialise the result.
- Copying an interface for the purpose of providing a compatible implementation (what Google allegedly did - although of course part of the debate is whether they also copied any of the implementation)
- Copying parts of the implementation, not for the purpose of compatibility (what faker.js did - in this case, copying constants)
IIRC US copyright law gives very little protection to compilation of non-copyrightable data (look up copyright status of telephone directories). The argument is that it's just public domain factual information bundled together.
The faker libraries are all that -- compilations of mostly non-copyrightable facts.
I'm not saying faker.js did no wrong, just saying if hypothetically a purported copyright owner sued him, they would have a really hard time proving substantial infringement happened given the available precedents.