At some point I started believing in something like a Gell-Mann Amnesia but for people. You talk/listen to this seemingly intelligent person who seems to be so

At some point I started believing in something like a Gell-Mann Amnesia but for people. You talk/listen to this seemingly intelligent person who seems to be so confident in his field. Or rather in one of the fields. And then this person starts talking about something completely different and he can't be more wrong. The question stands now how much doesn't he know about his own field which he also seems to be so confident about. E.g. some philosopher psychiatrists starts to give some dietary advices of only eating raw meat. You would think and overall intelligent person should not be giving such advices. So can we just ignore him as dietitian or should we also start questioning his views as a psychiatrist.