World War 2 Re-enactment German soldier talking on phone

This photo which was taken at a World War 2 D-Day re-enactment shows a ‘German soldier’ talking on a modern mobile phone or cellphone

It seems pretty bizarre to be using a modern form of communication like this at an historical event like a World War 2 re-enactment – isn’t there a conflict here?

World War 2 re-enactment German soldier talking on mobile phone or cellphone