While there are grammar rules (people can recognise something as ungrammatical, even if they understand it) There are very few, if any, strict rules about meaning.
If a phrase of English has had the intended effect (of communication, of persuasion, or of beauty etc.) then it is correct.
The usual idiom is to "coin a word". This was developed from the original meaning of "make a coin". Since the 1940s we have been saying "coin a phrase". I see no great problem in further extending the meaning to "coin an idea", especially when the idea is closely linked with a particular word "BRICS".
The meaning of the paragraph is clear: "The word and idea of considering the five largest developing economies was invented 20 years ago". English is flexible enough for extended meanings of words to be used, in context, all the time.