Can you provide us with data to support your claim?
Work Ethic is a non-quantifyable factor, so obviously he can not beyond polling data.
What he could provide, if he wanted to do the work, is the Workforce Utilization and/or other figures that detail the % of the able-bodies population who are working. That would, of ocurse, not be 1-to-1 for "worth Ethic" but it does tie into much of the same ideals.
Conversely, since the issue is a non-material item, can you provide any source that would contradict his claim? Polls, studies, etc, that state Germany does not, in fact, have a high work ethic nationally?