I wonder if it is a metaphor here, though. If it was written by an American, then I would undoubtedly agree with dojibear, but the expression does not exist in BrE, and I have no idea whether there is a similar expression in Dutch. I think it unlikely a translator would have introduced a metaphor into the work if it had not been there in the original.
My guess is that Sam Salomon literally lived on the other side of the railway line from where Anne Frank lived.
I looked up the quote. She's characterizing several of the boys she knows. I'm pretty sure it's the metaphorical, not literal, wrong side of the tracks. It's a fairly common expression in U.S. English, so an American translator probably wouldn't hesitate to use it to express "from the bad part of town."