Due to the similarity of German and English, German speakers can superficially appear far more competent in English than they actually are. (This goes both ways.) Speakers of both languages come to the other with about half of the grammar (including hard bits that usually betray non-natives like irregular verbs by vowel umlaut) and a large collection of basic Germanic roots.
I'm always amused when watching a German film how entire sentences sometimes are decoded by my brain as English, when they're German.
But this completely breaks down once you go beyond "Ich habe all das Bier getrunken". German never got all the French-Latin vocabulary. Most technical and literary terms are completely different. They may feel quite ill-at-ease in English even though they sound reasonably fluent with the basics.
Sadly, this style also makes my English bad^^
It looks like a cultural to me, in many times when I have interacted with people from Germany in a business context it just seemed that they are perfectly capable of speaking english but they just don't want to.