You are.
The first thing you missed is that no one told you that the graph on the client page is all but meaningless. Don't pay any attention to it. All the ratings are completely arbitrary and frequently don't make any sense.
To answer your question, which I presume is "What kind of items do I build on Alistarm AD or AP?" The usual answer is actually neither.
The second thing is, since a lot of the strength of Alistar's kit is independent from the items he builds, he is frequently taken as a support where he does not take farm but instead focuses on assisting carries and builds utility items and a some survivability.
Now, that's not to say Alistar has to build that way and cannot do something else. There are plenty of videos out there where people show off alternatives for Alistar such as https://www.youtube.com/watch?v=rvBjnFLdnxs AP Alistar builds or https://www.youtube.com/watch?v=SI1aDtYac4c&spfreload=10 Tank Alistar in Top Lane. It's just that in competitive play people usually take him as a support bot lane because he is good at it and his utility there is why.
(Also, because where Alistar is good outside of bot/support tends to get nerfed out of existence, but that's a separate matter.)
is more on AD but on the eSportspedia wiki, 
