Despite having the same name, Satish Kumar and Satish Kumar are different people in the book. Pi takes a moment to explain to readers that both names are quite common, so it didn't surprise him that two very influential men in his life have the same name.
The first Satish Kumar that Pi tells readers about is his biology teacher. He is a polio survivor with an oddly shaped body. His physical appearance makes him stand out, and that is a physical difference between him and the second Satish Kumar that Pi tells readers about. The second Satish Kumar is so regular in appearance that Pi tells us that he always has difficulty recognizing him.
The two Kumar men are also quite different in their religious beliefs. Kumar number one is a staunch atheist, and this surprises Pi. They discuss God and religion, and Kumar passionately defends his own beliefs. While Pi doesn't agree with Kumar, Pi is able to learn much about himself and belief systems from Kumar.
The same can be said about the second Kumar as well. He also is deeply influential in Pi's life, but Kumar number two is a deeply religious Muslim. His words and actions will eventually help to convert Pi. The two Kumar men also love animals and the zoo. While their reasons are different, they still appreciate the world/creation that they get to see up close at the zoo.