I just think it was badly explained to him. By the edit you can see that it is in fact payment in arrears. By all means, I think it is not normal in IT. But it is a normal practice overall anyway so nothing to worry about
@fireshark519 Yes. "A week in arrears" is much clearer than "first week's pay withheld indefinitely". (Also, it's not the same thing, as salary can change.)
@TRiG well yes I understand the concern, if it was EXACTLY the first week that they put aside then things like interest should be discussed. As it is a rolling week, not really. Just bad HR explanation that's all