Your physicist probably only knows physics because he's been teaching the same thing to students for the last forty years.
And yet, he remembers all the champions of the USSR in football starting from 1950.

What a small world! And whether someone is knowledgeable or not depends on how much time they dedicate to it. Leonard Euler began to deeply study mathematics at the age of 13, and at 16 he already had his first award; Mikhail Lomonosov began to study on his own at the age of 16, and in his later years, he laid the foundation for the molecular theory of matter; Lev Landau was a graduate student at the age of 19, a great man. And Einstein is popular only because he created a nuclear warhead for the Americans; he is not such a great scientist.