What does the phrase "strictly so called" mean here?
Solution 1:
Strictly can mean 'exactly or correctly', and so-called can mean 'thus named or called', so the second part of Adam Smith's lectures comprehended (covered) ethics according to a very precise definition.
It is worth noting that 'so-called' is the modern hyphenated usage, and the modern usage tends to have a sneering implication that the 18th century writer did not intend.
Strictly (Cambridge Dictionary)
So-called (Cambridge Dictionary)