Yes. It is not literally true. Nonetheless, I'd bet students of Nobel winners almost always show significant promise. Moreover, they're likely working in areas where Nobel prizers are likely to be won- what I mean is, there are some areas in any given field where work is likelier to yield a Nobel, even controlling for the quality of the work. In Physics, for example, Nobel's are rarely awarded for the more theoretical work on less established subjects. So since the students of Nobel winners are usually in the same fields it makes sense that they would have a high then average likelihood of winning one as well.