They use weighted average of past performance. Its certainly not based on 1 year of data. Zips projects 149. Most players would take his "down' year.
What do you think he's going to be over the next 3-4 years? You don't really project 120ish, do you?
I'm aware of what they use. I would predict a 120-135 range which is what he's done every year besides one so far.