I think at this point no one really knows the context, it just sounds cool and is better than using a common superlative.

The reason is kinda fits it just because the root word was been used a lot in religious contexts without a specified ontological basis (since Christianity is implied). Which means that people are using it that way without the Christian context. Which initially makes it confusing, but if you just slot in “Facebook Zeitgeist” as your ontological basis, it actually makes sense even if that wasn’t the intended use.