Just to help your understanding . . .
A husband comes home and asks his wife, "Hey Honey, do we have any ham in the refrigerator?". The wife answers, "I don't believe so".
From that exchange, what can you say about the wife's beliefs about ham being in the refrigerator? Is she saying there is definitely no ham in the refrigerator? Doesn't sound like it to me. It sounds like she doesn't think there is any ham in the refrigerator, but she is also keeping open the possibility that there could be ham in the refrigerator. However, she lacks a positive belief that there is ham in the refrigerator.
The wife would be an ahamist. If the husband opens the fridge and, lo and behold, there is ham in the fridge, the wife would probably shrug her shoulders and say, "Guess I was wrong". She would then become a hamist when faced with the evidence that there is ham in the fridge.
Does this make sense?