Afew of the news reports were slightly off. Bydgoszcz is actually the 8th biggest city. It's about 2/3 the size of Dublin so it is totally possible that he got separated from his friends there and couldn't find them. If he assumed they had left for Poznan without him it is likely that he jumped on a train to Poznan. After that they were looking for him in the wrong city.
The story about the train to Berlin is strange because he would have been asked for his ticket several times on the train so he would have known he was going to Berlin.