I'm glad you caught that one and pointed it out. I would have to agree with you, but how many people believe this or do it without having a discussion. It wouldn't be my first recommendation for the following reason.
First of all, molds/fungi are tenacious parasites. In one of those studies that I posted 2-3 fungi were found in the cavity (again, you can always find more than one parasite in congregation)! A stream of water through the nose won't truly relieve the problem. It may help with clearing away some of the mucus, but not the parasite(s). Additionally, there is the likely event that the fungi could be driven further into the sinus cavity via water transportation.