Meditating on knowledge, I think it’s fair to say that there are two ways to ‘know’ something. It can either be reasoned/figured out in real time, or it can be looked up from previous experience (Cached Thoughts). The vast majority of our life experiences are repeats of previous ones (sometimes with slight modification) and our understanding of and responses to these experiences is usually recalled from memory without any thought.
True intelligence, however, is not the recall but the ability to create knowledge where it does not exist yet within your mind. It is reasoning, logic, etc. This takes longer to do than a simple cache lookup, so it may be fair to say that if someone is quick to come up with a response to a difficult problem or situation they are not necessarily smart but merely experienced.
One can improve their intelligence with practice; by trying to manipulate objects, situations and problems in their mind, to test and try new assumptions and view the situation from those alternative realities/perspectives. Being aware of logical fallacies and biases can save you time by avoiding most branches of thought when analyzing a problem.
Finally, as underscored in the post linked to in the first paragraph, be wary of cached thoughts. They are many times planted without much analysis and can effect your thought process in ways that are hard to spot. It is helpful to frequently reconsider cached thoughts that you rely on heavily, no matter how popular they appear with other thinkers or how effective they may be at predicting the specific phenomena you have been leveraging them for (it may not generalize!); false confidence is the enemy of a true thinker.