I suspect it is the difference between "coding ability" and "coding fluency." In the former a candidate can apply known patterns of a give language to a problem and with just a few searches on StackOverflow get it working. A person who has code fluency can create the algorithm in the language of your choice, pretty much on the spot.
In the music world you meet people who can play a song on the keyboard that is note perfect, but they can't transpose it into a different key. Its the difference between playing the keyboard and using the keyboard to express a musical concept.
Can you speak a language if all you have done is memorize an extensive phrase book? Yes, are you fluent? No.
The number of candidates who really understand the nature of coding and so they can quickly adapt to any idiomatic language is still quite small in my experience.