The key element that you're missing is 'and brushed up on the fundamentals.', nobody is saying that Skiena is the only source you should be learning and that you only need to know what is in that book.

How I read recommendations like that is that it is probably a book that gives a good overview of the different topics that might be relevant. Of course for every separate subject there is probably a better resource, but that's not the point.

Preparing isn't the same as going about and learning complete new things, preparing is making sure that all the stuff you've learned in the past is fresh in your memory and ready to be used. In which case a book that gives you a quick overview does the job perfectly.