I don't think that there is clear recommendation which query language to use. In the end the they are executed both within the same query engine, and the result and the performance are the same. Also Adobe-internally I can say that we use both query languages without really being in favor of any.
Historically there's been a favor of xpath (I don't know the reason why), and xpath has been deprecated during the standardization of JCR2 (as not only Day Software was involved, but also other companies which were favoring SQL/SQL-2). But xpath support has never been removed from Jackrabbit and Oak, and it's still fully supported.
So regarding your interview question, I think that statement of the interviewer was not really correct.