Any connection between any GE experiments and the E. coli strain in Germany is pure speculation.

The bacterium is most useful in cloning experiments, used in recombinant experiments, it is a choice because of its small genome size, the first to be sequenced. It has long been used in the biotechnology industry.
Other useful properties are its fast growth rate and nutrient properties. In humans, it provides vitamin K and B12.

One particular strain was infectious- now two are known. The source, possible mutation, combination with other bacteria, etc., are some of the avenues of research that must be pursued.