could listen to a piano

[keannu]

Do these two "could" mean conditional mood or just presumption(lower possiblity than "can")? I sometimes get confused when I see "could" with merely a subject.
Does it mean conditional mood like
"If it were a person, he could(meaning "can" in the present) listen to a piano concerto.."
or presumption "His ability to listen to a piano concerto is lower than the nuance of "can" " I think it's the former, but sometimes it's confusing to tell.

It's like this. "He could come to the party"
Does it mean "It it were him, he could(meaning can in the present) to the party"
or "His coming possbility is lower than normal chance"

ex)Savant syndrome is a condition in which a mentally disabled person shows brilliant abilities. In fact, the word "savant" means a gifted person. People with savant syndrome often have amazing memories. For example, one could listen to a piano concerto just once and then play it perfectly. Another could memorize every dialing code in the country..

[5jj]

This probably means that one was able to .... and another was able to ... . However, it is not impossible that it means 'one might be able to ... and another might be able to ... . We cannot be sure.