Well, you get some things mixed up here. There was a coachbuilder called Pio-Karosseriewerk in Hamburg-Fischbek. He built the "IGA-Eisenbahn", IGA stands for Internationale Gartenbau-Ausstellung (International gardening exhibition), which took place in Hamburg in 1963 and 1973. That is the railbound train in the black and white pictures you posted. The picture with the 5 trains show three different types: the three trains to the left were built after the puzzle train by another coachbuilder (Sollinger Hütte), the fourth car is the puzzle train and the fifth car is another train, presumably built by the same coachbuilder as the puzzle train. There is a hint to where those two were built in the source you found, though.