There are other reports of hundreds of deaths that were simply not tested for the virus, whereas in Italy they've tested pretty much every death since the outbreak in February. Considering that Patient-0 was infected at the end of January, the theory that there might be some under-reporting going on is not unrealistic. Germany probably just had the capacity to deal with this "under the radar" for longer than Italy.
This is hardly unique to Germany, btw - each country has adopted different methods to test and report, it will likely take time to get some decent convergence at European level.
First: I hate twitter.
Second: in a follow up he seems to say (using google translate):
> It is EXACTLY what I meant: they charge the deaths to other pathologies present. I don't see many other possible explanations.
So he doesn't have proof or even a statistic to point to? He just doesn't see an alternative explanation? Is the newspaper he is working for yellow press?