When someone gives their version of events in a trial, tribunal, disciplinary case or whatever, that is evidence. The fact that there might be other evidence that contradicts it doesn't stop it from being evidence.
Day in, day out, hearings take place where it's the task of judges, juries, panels etc to decide between two or more witnesses giving conflicting oral evidence, and they have to decide which is more credible from things like their demeanour, whether they have motivation to lie, what is standard practice etc.
Think about, say, a case involving someone being knocked down in the road where the only witnesses are the person who was hurt and the person accused. The accused gives oral evidence that he was driving slowly and paying attention and the injured person ran out into the road in front of him, the injured person says he crossed the road with due care and the driver was speeding and paying no attention to his presence. Before the police get there there is a torrential storm that wipes out any evidence on the road. The statements of each of them are evidence and the judge will have to decide which of the two is more credible on a balance of probabilities - and will take into account things like the demeanour of each witness when giving evidence, whether they have been caught out in any inconsistencies, any previous record, the road conditions at the time, and so on.
In Fulcher's case, the panel decided that they found Pritchard more credible than Fulcher. That may be because of their respective demeanours when giving evidence, because they accepted that it would have been standard practice to give a warning about going to the press and it was highly unlikely Pritchard would have departed from standard practice, because they thought it possible that Fulcher had forgotten or wasn't paying attention, or did hear it and made a deliberate decision to ignore what he was told - or because they were constitutionally disposed to believe the more senior officer and wanted to "get" Fulcher. Whatever their reasoning, there was certainly evidence.