how can the houyhnhnms be role model for human being

Houyhnhnm society represents an idealistic society. They are driven by a sense of benevolence and work towards the betterment of community. They are even aware of evil. There is no corruption. They only die of old age and accept death as a routine phenomenon. They are clean, well-kept and contented with their lives.
 
On the other hand, in the society of human beings, many complexities arise out of our negative emotions, such as selfishness and greed leading to social malaises like corruption. Humans strive to eradicate these problems, but, never reach perfection.

Thus, Houyhnhnms can certainly be considered as role model for human beings.