Was this math? I found usually math guys including professors like to talk about math.

In my experience, when they're top tier math researchers they tend to be oblivious to the student's perspective, grasping the problem too well to give it detailed treatment. This is neither a failing of their enthusiasm nor a social tactic, but an imbalance in their abilities.

An old anecdote is the professor who was asked by a student how a certain problem is solved. The professor paused in thought for a moments, then gave the answer. The student asked again how to solve it, and the professor, again, thought for a while and gave the answer.

The student persisted: "but how is it done?" To which the professor gave a frustrated look and said, "I already solved it two different ways, what more do you want?"

University lecturers in particular are a deluded bunch. They mistake their role for one of power and forget that the students are their employers. Source: 100 years as a University lecturer.