Depends on the context.
A scientist or somebody doing knowledge work should be bumping up against "I don't know" daily.
I think not knowing becomes problematic for (say) an emergency room ER.
Discussion
Are you saying that if someone never says "I don't know", but they work in ER, then they are (or can be) intelligent?
I would say that expressing uncertainty in that context is probably bad. When seconds count, decisive action needs to be made. IDK if that maps to "intelligence" exactly though... more like training / competence?
You're talking about specific incidents.
What I'm asking about is, if someone NEVER claimed to be ignorant.
If someone always pretended to know the answer to absolutely everything that was asked, would you consider that person to be intelligent?