JoelOnSoftware had a great piece back in the day where he mentioned that while he consciously knew what a short sale on an option was, in practice he had to stop and think about how to calculate it, while his financial friends just knew the answer immediately. He drew a comparison to pointers in C, where if you're going to be a C programmer, then pointers should just be intuitively obvious to you and not something you need to think about.

IAW, there are no pure fast or slow thinkers, a lot of this is just how well have you internalized the background material. Having quick repartee in conversation has absolutely no relationship to immediately seeing what the loop variable should be in a programming problem. FizzBuzz isn't quickly solved by decent devs because they think faster, it's quickly solved because it's a trivial problem that doesn't require serious thinking for experienced devs.

When I'm programming for finance or medical, I often have to tell the PM "let's stop here and let me think about this for a day". Because it's not my field, it takes me a while to get my head around it. OTOH, there's very often algorithm conversations where I have to wait for others to catch up.