Hi Jochen,
SUPER interesting find, thanks for pointing this out, Jochen.
To me, this looks like Google understands that these two pages are the same page, except for different devices, and is using information on the desktop page to make their search results more robust for mobile.
You can see the connection by looking for Google's cache of your mobile page. The best way to do this is to search in Google for "cache:[URL]". If you search for "cache:http://m.avogel.ch/de/ihre-gesundheit/erkaeltung/alles_ueber_erkaeltungen.php", Google will send you to the desktop version of the page.
Here's my theory: Google has one index for both desktop and smartphone users, so it combines data and gives the user the best result possible. Google's doing more and more to try to improve its search results even without SEO intervention, so I'm not too surprised about this, but can't seem to find this in any SEO articles out there.
In answer to your question: I recommend that you continue to keep you mobile and desktop sites similar enough that Google is pulling from both. In the past, some SEOs would build sites differently for mobile users, but I've never seen any UX studies that shows that that's a better approach. Given that Google strongly recommends that you use responsive web design, it's certainly not Google's recommended approach.
I hope this helps? I'm not sure if this was a post because you were worried about something - this seems like good news to me!
Kristina