Copenhagen-Frankfurt-Shanghai-Frankfurt-Copenhagen —> 144 hours visa?

A friend of mine has previously used th 144 hours visa option to visit me, but back then we did Copenhagen-Shanghai-Hong Kong-Copenhagen. So clearly fulfilling the rule. This time we are thinking of a flight from Copenhagen to Shanghai with a stopover in Frankfurt on the return ticket. Would that comply with the rule or does the third country need to be a real stay and not just a stopover on the way back? Thanks!