A plantiff did not attend the hearing. Consequently the adjudicator dismissed his case. What does this mean? I roughly understand that it means the defendant is absolved of the charges and that the plantiff can not reopen the case (or charge for the same thing again) without proving he had a very good reason for missing the hearing (e.g. was in a hospital).
Not necessarily. It depends on the type of dismissal.
The term prejudice helps better describe your question.
You have described a dismissal with prejudice: the case can not be re-litigated.
But it's just as likely the case could have been dismissed without prejudice. Meaning, the plaintiff could restart the case at any time. Or, alternatively, file a new case on the same facts. (You might be thinking about double jeopardy which is prohibited and applies to criminal cases involving an acquittal.)
The with prejudice vs. without prejudice decision is often left to the discretion of the judge (or adjudicator) depending on the type of proceeding. And sometimes the decision is determined by procedural rule.
You must read the notice or order of dismissal to determine what type of dismissal it was.