This all seems a bit silly. Sneaky Company, Inc. can also add in that this new clause should be removed.

The problem here isn't the legal interpretation of the license and adding new clauses doesn't seem to do anything useful. Sneaky Company can license their software under whatever weird combination of terms they like. If they want GPL except it's proprietary then they can do that. Weird but ok. Same again if they want the license to be internally contradictory - seems stupid but they can do that too.

The actual issue is if they're trying to be deceptive by framing something as GPL licensed when in fact it is some new not-in-the-GPL-spirit license that they have developed. They should either be generally shamed or sued by whoever has copyright over the term "GPL" (pretty sure that is the FSF). That'd be ironic but there you go. Or some sort of false advertising suite.

FSF did the shame thing:

https://www.fsf.org/blogs/licensing/agpl-is-not-a-tool-for-t... https://lwn.net/Articles/1067771/

Contract law has Contra Proferentem ("interpretation against the draftsman") principle, Ambiguous or confusing contract is interpreted against the party that provided the wording.

If Sneaky Company makes weird and confusing license, it's interpreted against them.