This is in contrast to research on the subject. Intelligence is one of the very few psychological properties that's universal. A smart person is smart. Doesn't matter the subject.
Of course that doesn't mean they know everything. It means that either they are smart and know a lot about a field OR can become knowledgeable a lot about a field in relatively little time.
This does also mean the reverse: expertise in a field does not actually require intelligence. It just works a lot faster if you have it. But being "dumb" does not place an upper limit on how capable you can be in a field, you'll just have to work longer to get there.
Of course that doesn't mean they know everything. It means that either they are smart and know a lot about a field OR can become knowledgeable a lot about a field in relatively little time.
This does also mean the reverse: expertise in a field does not actually require intelligence. It just works a lot faster if you have it. But being "dumb" does not place an upper limit on how capable you can be in a field, you'll just have to work longer to get there.