Your dad's results definitely point to one fully Ashkenazi grandparent as the most likely possibility. When this is a surprise, usually it's a grandfather. The most likely scenario is also that one of your father's known grandfathers was not his biological grandfather; this is referred to as an MPE (misattributed parentage event). I personally would not trust MorleyDNA because I've heard haplogroups aren't always correct. If possible, I would have your dad do the following:
I say all of this as a professional genetic genealogist who specializes in Jewish DNA cases such as these. I'm also the moderator of the Jewish genetic genealogy group on Facebook.
If you have any questions, please let me know.