Perhaps even more than the crossbow issue, what sticks out is Nobunaga's insistence of getting his hands on the Art of War, by Sun Tzu. The thing is, those teachings WERE known in Japan at that time, studied by Japanese commanders, and the daimyo Takeda Shingen, contemporary with Nobunaga, for example, could almost be considered a scholar on the subject...
There are also several sources that state Nobunaga actually did study those teachings, along with Toyotomi Hideyoshi, and Tokugawa Ieyasu.