It is German LE that are placing great significance on this call, are suggesting it puts his phone in the area and are keen to speak to whomever it was that that phone called.
I assume they have reasons for this gleaned from use of people with expertise on phone masts, coupled with whatever other pings they may have locating his movements. Even 2.5 miles error is significant given the time of the call and how easily he could get to the crime scene in time.
My friend recently did jury service on a stolen treasure trial in the UK. Most of the case against the defendants was based on phone pings placing them at certain locations with a degree of accuracy that allowed a guilty verdict.
So if you're concerned about German LE and the phone data it's them you need to take it up with.