It’s both really if you look at IQ tests. It’s part of the reason immigrants will often score lower, they lack the culture or language specific knowledge being tested.

IQ is a proxy for intelligence. People often use them interchangeably, but they’re not the same thing. Your statement is more valid for intelligence than IQ.

It’s not just that its the ability to reason in different modalities without specific knowledge, as well as others. Speed is certainly a part, but not the only part, of the IQ text.