Well, if it isn't binding, then there's no right to reuse it (beyond certain fair use exceptions) under the copyright law that applies by default.

For me the question is whether the misleading blog post would be found by a court to be an implicit license separate from the one in the codebase. My guess is that it would depend on several factors including the specific circumstances of the accused infringer and the specifics of contract/copyright law in the relevant jurisdiction, but probably at least sometimes yes.

TIL something can be implicitly licensed. Well the term is implied license https://en.wikipedia.org/wiki/Implied_license

An open source licence generally only gives additional rights. If it's not binding, then default copyright would apply, meaning you're still not allowed to use it.