The narrator is surprised to discover that Pi is married in Chapter 30 because he had never seen any traces of anything other than a bachelor existence in Pi's home up until this stage. The narrator perhaps assumed that, after Pi's traumatic experiences as a castaway, he would find it impossible to form "normal" human experiences and to settle down in a standard family. He therefore assumed that Pi was a solitary individual who lived by himself. When he is introduced to his wife, however, he begins to look around him and re-evaluates what he sees:
This house is more than a box full of icons. I start noticing small signs of conjugal existence. They were there all along, but I hadn't seem them because I wasn't looking for them.
The narrator is therefore surprised by the family life Pi leads because this didn't fit the mental picture and assumptions that he had made about Pi and the kind of way he would live his life now, so many years after his experience. It is only when he knows of Pi's wife that he is able to reassess and begins to see what was in front of him all the time.