Yes it comes from a speech made by the Kaiser. I can't get it right now but I'll send you a link in a few unless someone beats me to it.
Follow-up: the question about German soldiers being called "Huns" is frequently asked and the standard answer references a speech given by the Kaiser in 1900. But this doesn't really answer exactly how an expression from a speech given fourteen years earlier came to be a commonly-used epithet for Germans in 1914 (if that's when the practice started). Was the use of the expression popularized by a famous writer or something at the start of WWI?