Is recomnder systems part of computer science?
The algorithmic part of the  recommendation systems is more closely related to the computer science, the theoretical part of recommendation systems is mostly combination of statistics and linear algebra, thus we can think of recommendation systems as the combination of statistics and computer science, and the data science is the field that one would actually call the combination of statistics and computer science.
Thus my take on to answer the question is that the data science is the field you are looking for.