There are other aspects as well. Much of them have to do with managing the load up times of the mental model of the topic at hand, with focus, but also setting up/starting correctly.

Quickness

Some people pick up things very quickly, others take a while to pick them up. Neither is necessarily "smarter" because they might have different thresholds to what they consider "getting it". The depth that they pick some new thing and feel they "get it" might be different. Additionally, how well they grasp it might be different levels in terms of when they feel they fully grok it. Smart or skilled on something is holistic understanding, the speed isn't always as important but is definitely helpful. Like learning something with prototypes rather than a big sprawling project, the former will be faster.

Longevity or Ability to Stick With It

Another aspect is people that pick up skills and how much they want to use them. If you quickly get skills, that may also mean you get bored with the skills/knowledge quicker. The people that work harder at it or have a deeper threshold or attainment level of how they "get it", may work with that more because it took more effort to grasp or the more they iterate on it the more depth/detail/interest is found.

Some people will be able to stick with something they get longer, others may want to move to the next thing. There are all sorts of variables with this: time, goal alignment, need, survival, effort, results, groups you are in like if it was for something personal or at work etc.

Self Starter

A key aspect to smartness is being a "self starter", one that looks into things driven by interest or potential need. The ability to just start playing and prototyping is a great skill to have.

Ability to Finish

On top of that, setting things up to easily ship is another way people can be professional. When you start a prototype but get the line to production setup early, the work you do will take less adjustments and make it easier to ship when needed. Right after a prototype I like to setup tools/games/apps all the way to the end on device, different platforms, different styles, basically two of everything so that issues you run into are already smoothed. This makes it easy to ship.

Simple to Approach

I like concepts that are simple to start, and potentially advanced long term to keep interest.

Since I make games and tools I like the "easy to approach, difficult to master" aspect of things and try to create that in my productions. I like the game/tool to be a "friend" so you like using it and it isn't tasking. That is another aspect, how much effort is required.

"If you can't explain something in simple terms, you don't understand it." -- Feynman

Iteration, Practice and Deeper Dives

Most highly skilled people are smart, of varying levels of speed, but the ultimate way to build skills is the repetition and iteration of consist creation/production and shipping. A deeper dive. The more detail and depth the better you can do it "simple". I usually judge people, at least in games, as what they have shipped. Sometimes I am amazed at how those people that produce come to the result, some get there fast and others are constantly re-learning, both have their benefits.

A Beginners Mind

A "beginners mind" or Shoshin [1] helps to refine that and keep things simple/approachable, which I think is the main goal of creation/production. I also believe the job of engineering is taking complex systems and making them simple, but still allowing the advanced users access to highly customize or use deeper features. This technique also makes it easy to come back to work on something years later that doesn't take a long time to load up the mental model.

[1] https://en.wikipedia.org/wiki/Shoshin