Frequency indication in Dictionary

I read it in the below page.
A marks the least frequent words, Z the most frequent ones.
I extracted en_US.dict file. Please let me know the terms like B, C, F, O,… in the frequency. Are the suggestions listed based on the frequency??

Firstly, they are based on the edit distance between the user’s word and the word in the dictionary. The frequency is only used as a second criterion, I think.

Thank you for your reply.