It is possible to have different logins at the waze map editor and the forum, I am an example. As far as I know there are at least 3 independent databases: the main waze features (mobile client, map editors, dashboard, etc.), this forum, and wiki. By default all logins are same and I am not sure if a user may change any login but the support may. My suggestion is to contact the support and ask them what they did.
It happened to me that when I installed waze and created my account the wiki account has not been created. Also I have found some wazers missing from the list of all wiki users. Could it be possible that the same occurs with the forum and an account has not been created for this wazer?
My previous login name was rl_pl.