Your son, probably has a good memory for rote things or good visual memory.
Then there is actual "comprehension" of abstract concepts and formulations... and analysis of it.
Then there is: fine motor skills and gross motor skills.
All of these things are, abilities "mastered" per the individual and development.
Then there is emotional development and social comprehension.
This is not, having to do with "academics."
But it is also a kind of "smartness" and acquisition, per development.
Reading is taught by phonics and sight words nowadays.
And the parent reading to the child.
All of this, goes hand in hand with each other. As a whole.
Main thing is that the child enjoys it. And that the child's cues, are matched.
All of these aspects, develops, in stages. And does not necessarily occur all together at the same time. Concurrently. Some "abilities" are mastered first, then other abilities.
Doing something, but then having comprehension about it.... are two different matters.
For example: in reading a simple story... of course you are seeing if the child can "read." That is word recognition and sounding out letters/words/word groupings. And then... there is the comprehension of it. ie: can the child "summarize" what the story was about, answer basic questions about the story/characters/main point of it...and the chronology of the story? For example.
These things are taught in stages... per school/grade level/age. And the complexity, is per grade/age level/school curriculum/ability.
Then, there is: can a child/student ASK questions about the story too, or what they read or what was read to them??? In order to find the answer?
And then, per a story read in a book, there is the emotive.... concepts of the story. What IS the story conveying??? What do the punctuations in the story mean... toward the characters and situations in the story????
Knowing that, is also an aptitude and comprehension. Not just rote knowledge.
Then there is: acquiring "vocabulary" AND knowing the definition of it, but ALSO understanding.... what the definition means.
My son for example, though he was only in Preschool and not fully reading yet... he knew and understood and used... big complex vocabulary. And he was, when younger, speech delayed. But he has a very prolific sophisticated vocabulary. And comprehension of stories/vocabulary and its uses.
So there is rote learning and "problem solving" about what they learned. And 'analyzing' what they learned.
But what is also very important, is the non-academic learning. Meaning, the emotional and social development of the child. Knowing how to "discern" people/play mates/social situations, and knowing how to ask for help when needed etc. Whether or not that has to do with academics or not. A child, needs to learn this. Of which, Preschool is the petri dish, for that. Not just for academics.
Some kids, are academically vibrant. But they lack the emotional APTITUDE and social aptitude, for their age.
Smartness is multifaceted.