Yes, that is true. He really did not care about it. The paper he wrote is Mendelian Proportions in a Mixed Population (http://science.sciencemag.org/content/28/706/49.full.pdf+htm...). It is brief, barely a page in length, and he introduces the HW equation with the preamble "A little mathematics of the multiplication table type is enough to that in the next generation the numbers will be [equation]".