What you experienced is known as "retrospective diagnosis" and generally speaking, is more about misplaced positive thinking than anything else. Often, but not always, the context is to say, "this person had X, Y, Z and they became ... did .... etc." Lincoln is a great example of this. A cursory review of identifications or diagnoses by modern educators, historians, and/or doctors suggest Lincoln was a depressed, bipolar, mentally ill man on the Autism spectrum with Marfan syndrome. He may have been all of those things. He may have been none of things.

It's possible to look at some of Lincoln's behaviors and traits and put them under the umbrella of Asperger's. Asperger's, though, didn't emerge an identity on the Autism Spectrum until this century. Its namesake, Hans Asperger published his work in the 1940's and even today, autistic people and medical experts question some of his criteria.

I suspect what your teacher or professor was trying to get to was that history is full of people who reflect the full continuum of neurodiversity. Some of those people have had positions of power and did great things. Some of them lived ordinary lives and did ordinary things. Some were treated as mentally ill and separated from their families and lived a live of isolation. The challenge for us looking back at their lives is to sit with the discomfort of never knowing their full story. You may find this on the concept of presentism from the FAQ's interesting.