You are very correct on the meaning of the name "Arocho." By the way are you aware that there is a village in Andalucia (Spain) called "Arroche" which is arocho in french. It seems that your father is correct in that the name originates from Southern France and the Northern Privinces of Spain
I found the last name "Arocho" in records in Puerto Rico, Cuba, "Texas", US Virgin Islands, Guatemala, and Canary Islands. Other forms of the last name can also be found, i.e., LaRocha,Arocha,Manarocho,etc. As a matter of fact you can find the troops with that last name on muster records in Texas of the Union Army during the US Civil War.
However, I have not been able to find out yet where my family originated. My paternal grandfather was born in Adjuntas, Puerto Rico and from what I understand his family was from a barrio of Ponce in southern PR-that is as far as I have gotten so far. The last name Arocho is not a very common name. Maybe I should add that I have seen people with the last name Arocho are listed on the passsener logs of ships from the Canary Islands to Puerto Rico in 1800s.
I hope the info is of some help.