So, looking at that thread, yes, you do need two function. You need an acf/save_post action in the admin and you need an acf/pre_save_post action for dealing with new posts created with acf_form().
These functions will work together.
In the admin, only the acf/save_post filter will be used.
For ACF form, first the acf/pre_save_post filter will be called. This will create the new post of the correct post type and return the post ID. Then a little later on the accf/save_post filter will be called to do all the other stuff that needs to be done.
Sorry for any confusion.
