I think that you are seeing the processes as considerably more restricted and linear than they actually are.
There are touch receptors all thorugh the body, therefore it is not surprising that they occur in the nipples.
Secondly only one of the hormones, Oxytocin, is actually released in response to the suckling.
Finally the fact that the article says that all these elements are required for 'successful lactation' leaves a lot of room for questioning what they consider 'successful' and allows a lot of space for many rudimentary mechanisms forming a basis for mammalian lactation which would not have satisfied the aticles criteria of 'successful'.
TTFN,
WK