gcap
When you operate at big airports you have to be able to fit in or IMO you should not be there. Part of fitting in is not unnecessarily impeding other traffic, that is just good airmanship. Crawling along at a slow speed on the principal taxiway with a jet behind you is not IMO acceptable. If I was in the GermanWings AirBus I most definitely would have politely but firmly indicated that your low taxi speed was causing me a problem and that I needed you to speed up.
Bottom line was the German Wings pilot was indeed an A**hole for being rude on the radio and you exhibited poor situational awareness and poor airmanship by unnecessarily holding up operations at a major airport
Not a great day for either of you......