From what I know about history, Hung Hei Guen's son, Hung Man Ting, practiced southern shaolin (aka Nam Kuen, aka Hung Kuen, aka Hung Gar, etc...) Perhaps he may have taught a little bit of kung fu in his travels, and his "students" may have put their own ideas or flavor into it. This might explain ha say fu's story.
Not commenting on the effectiveness or legitimacy of ha say fu, I believe it was evolved from hung gar, same as many other "tiger" themed styles. White tiger (bak fu pai) and Fu Jow Pai (tiger claw style) are all recent inventions with colorful histories, but in reality, they are based on a few techniques and ideas from southern shaolin / hung gar. Sifu Wong Kiew Kit of Malaysia also supports this claim.
Much of the village kung fu in southern china claims to be southern shaolin or go by the name of hung gar. Often what happened in the old days was a village would hire a kung fu master to teach the villagers martial arts for a short time, or the village might send a few people to go learn from a master. Often, the "master" was the only person around with any kung fu knowledge, which was usually very limited. Because of this you have all kinds of people with their own versions of styles, their own unique styles of kung fu, with little or no quality control. Just by looking at all the different types of so called hung gar/southern shaolin, you can see some of it isn't as "authentic" as others.
I know that San Dong Hak Fu (Shantung Black Tiger) became very famous for just specializing in the few tiger moves, and created their own style/school/group quite a while ago.
From what my sifu has told me, there is a gung ji fook fu doy dar (taming the tiger sparring set). Basically, it isn't even a "form", just a collection of very simple drills and techniqes. His opinion is to rather spend time on three star blocking, or Fu Hok Doy Dar.
I have noticed recently that on Lam Jo's son's site, they claim that their father created fu hok doy dar. I also believe this to be false. Didn't Wong Fei Hung choreograph this set with the help of Lam Sai Wing? Perhaps Lam Jo created his own version as well?