In this particular instance, the modal particle schon introduces a contrast to the preceding clause or statement, i.e. the meaning is adversative. I agree that the explanations given by Duden are somewhat lacking. However, the example under 6. can be rewritten to resemble the piece of dialogue you quoted:
A: Von der Tätigkeit her ist die Stelle nicht sehr ...
Sentences in spoken language are very often ellipses. An ellipsis is a sentence where you omit a part of speech that easily can be reproduced from the context.
For example, the first sentence spoken by Gustav doesn't contain a subject:
Macht nicht viel Sinn, Maik Grasser zu entführen.
Doesn't make much sense to kidnap Maik Grasser.
But every German ...