Well that approach seems interesting. However, a first issue is that Germany and especially the Germans are peculiar with data privacy and probably there will be an outcry in the media about such an approach. A second issue: How should one interpret the outcome of such an approach. Isn't is probable that the outcome will be something like: "These people visited public restroom frequently" or "have been at Pharmacies or Doctors". In short: How to distinguish cause and effect?
On the first issue: In a democracy, the use of data that has already been collected can always be used for other purposes as long as you have the right filtering tool in effect. I am sure Germany can find ways to set up a privacy commission that oversees the use of this data in times of crisis. Five hundred sick people and some twenty dead count as a crisis in my book.
On the second issue, I recall how John Snow discovered the source of a Cholera source in London: By mapping the location of the sick/dead people by their habitation.
Even he had to do additional thinking after having collected the data (use a diffusion model) to find the epicenter of the disease ( a water handle on Broad street). The way I see I see it, the authorities have no clue. We still don't know if it's in the water system, transportation system, airborne, foodstuff, everything is on the table. Throwing this new layer of information might put additional constraint on the infinite number of solutions they already have (an underdetermined system of some sort).
Of specific interest are the outliers: the foreigners and the Germans not living in Hamburg. Some of them were there for a short time and so are likely the ones whose locations are most interesting. They are probably the ones putting the most constraints on this underdetermined system.