Congratulations on discovering this match.
If the chromosome browser shows the two of them with very similar DNA, I'd say there's some mistake or confusion about the identification of these two DNA tests or about the relationship of these two testers in Germany. For example, maybe they thought you were asking about a different DNA test (sometimes one person manages multiple tests -- and I've had situations where a person got confused about which test I was asking about) or maybe they are parent and child.
It might be helpful to have a bilingual WikiTree member translate your message into German for you, so you can send your next message in both German and English -- to ensure that they understand you correctly. In your message, you could invite them to reply in both German and English so you can have a translation of their German message made -- in case their English message has a language error that causes confusion.