[owaislone]

I guess they mean "fork" in the broader Open Source sense when you fork something to create your own version of it and take it on a different path or do things differently like like NeoVim forked Vim. GitHub uses the term "fork" merely to create a copy of the repo for contributions.

[lifthrasiir]

The problem here is, of course, that the definition of "forking" is missing from the license. It is evident that two reasonable definitions for "forking" exist in this context (however you feel about Github's takeover of the term) and will continue to confuse potential contributors until fixed.